CHEMICAL  ENACTIONS 

THEIR  THEORY  AND  MECHANISM 


BY 


K.  GEORGE  FALK,  PH.D. 

HARRIMAN   RESEARCH    LABORATORY, 
THE    ROOSEVELT   HOSPITAL,    NEW   YORK 


NEW  YORK 
D,   VAN  NOSTRAND  COMPANY 

EIGHT    WAREEN    STREET 
1920 


Copyright,  1920 
D.  VAN  NOSTRAND  COMPANY 


PRINTED  IN"  THE  U.  S.  A. 


TO 

D.  L.  F. 


491336 


PREFACE 


THE  central  idea  of  this  book  is  the  development  of  a 
general  theory  of  reactions  which  will  include  both  in- 
organic and  organic  reactions.  The  fundamental  view  upon 
which  this  theory  is  based  is  the  "addition"  theory  accord- 
ing to  which  when  two  or  more  substances  react  a  primary 
addition  is  the  first  step.  This  theory  is  not  new.  It  has 
been  used  in  more  or  less  isolated  cases  for  a  number  of 
reactions  and  may  have  been  suggested  as  of  general  appli- 
cability. As  far  as  the  writer  is  aware,  however,  this  is  the 
first  time  that  it  is  published  in  an  extended  form  with 
modern  conceptions  of  chemical  structures,  which  them- 
selves rest  upon  the  development  of  valence  views. 

The  modern  interest  in  valence  appears  to  have  started 
in  1899  when  Thiele  published  his  paper  on  partial  valence. 
Some  years  later,  1904,  J.  J.  Thomson  suggested  the  basic 
ideas  of  the  electron  conception  of  valence,  but  applied 
these  to  very  few  cases.  From  that  time  on,  the  electron 
conception  of  valence  occupied  the  minds  of  a  number  of 
chemists  who  attempted  its  application  as  shown  in  sporadic 
publications.  Professor  Nelson  and  the  writer  believe  that 
they  were  the  first,  dating  from  1909  on,  to  publish  extended 
applications  of  the  electron  conception  of  valence  to  organic 
as  well  as  to  inorganic  compounds  and  reactions,  and  to 
develop  certain  lines  of  chemical  theory  from  this  point  of 
view.  In  the  development  of  these  views,  they  travelled 
over  a  certain  course  of  chemical  thinking.  Unquestion- 
ably, others  have  followed  the  same  or  similar  lines  of 
thought  and  reached  similar  conclusions.  Among  those 
who  have  published  along  these  Hnes  may  be  mentioned 
H.  S.  Fry,  W.  A.  Noyes,  J.  Stieglitz,  L.  Jones,  G.  N.  Lewis, 


vi  CHEMICAL  REACTIONS. 

R.  F.  Brunei,  W.  C.  Bray  and  G.  E.  Branch,  S.  Dushman, 
J.  Stark,  H.  Kauffmann,  and  a  number  of  others.  No 
attempt  will  be  made  to  give  a  historical  review  of  the 
problem  or  to  determine  who  is  responsible  for  any  par- 
ticular part  of  the  theory.  That  it  was  possible  for  certain 
workers  to  publish  before  others  does  not  negative  the 
fact  that  such  theoretical  views  may  have  been  taught  and 
used  in  planning  experimental  work  by  either  group  long 
before  their  publication. 

For  practical  reasons,  it  was  not  possible  for  Professor 
Nelson  and  the  writer  to  add  to  the  experimental  data  from 
the  newer  point  of  view,  but  it  seemed  at  the  time  as  if 
sufficient  facts  were  recorded  in  the  literature  to  permit 
of  a  conclusive  test  of  the  theory. 

The  electron  conception  of  valence  has  now  apparently 
been  widely  accepted.  At  the  same  time,  a  number  of 
chemists  still  speak  of  polar  and  non-polar  valences.  To 
the  writer,  no  useful  purpose  is  served  by  such  a  distinction. 

As  stated,  chemical  reactions  form  the  keynote  of  this 
book.  The  first  three  chapters  are  preliminary  in  the 
sense  that  they  treat  of  the  underlying  theoretical  concep- 
tions used  in  the  later  chapters.  Certain  parts  of  Werner's 
theoretical  views  are  used.  At  present,  these  appear  to  offer 
the  only  explanation  which  is  at  all  satisfactory  for  what 
have  been  termed  at  various  times  "molecular"  compounds. 
In  recent  years,  G.  N.  Lewis  and  I.  Langmuir  have  developed 
certain  conceptions  of  molecular  structures  from  the  point 
of  view  of  electron  distribution.  These  conceptions  are 
of  the  utmost  importance  and  indicate  new  methods  of 
formulation.  To  apply  them  to  the  consideration  of  chem- 
ical reactions  appears  to  be  somewhat  premature.  At  least, 
it  appears  to  the  writer  that  for  him  to  attempt  it  would 
be  so.  Since  their  views  are  not  used  here  and  since  this 
is  in  no  way  a  historical  treatise,  they  have  not  been  given 
in  detail.  On  the  other  hand,  it  is  believed  that  enough  of 


PREFACE.  vii 

the  general  theoretical  side  has  been  given  to  permit  any 
one  interested  to  follow  intelligently  any  further  develop- 
ments of  structural  chemical  theory. 

Questions  of  stereochemistry  have  not  been  included. 
It  would  appear  that  spatial  chemistry  is  entering  upon  a 
new  phase.  The  experimental  and  theoretical  work  on  the 
arrangements  of  atoms  in  crystals  as  exemplified  in  the 
publications  of  the  Braggs  and  of  others,  points  to  an  entirely 
new  conception  of  stereochemistry,  while  at  the  same  time 
stereochemical  explanations,  such  as  steric  hindrance,  which 
have  been  accepted  heretofore,  are  being  superseded  by 
explanations  based  upon  different  relationships. 

A  number  of  new  points  of  view  and  explanations  are 
advanced  here.  Many  of  these  have  been  presented  by 
Professor  Nelson  to  his  students  at  Columbia  University 
during  the  past  years.  Whatever  value  this  book  may 
possess  is  due  in  a  large  measure  to  him,  both  in  the  develop- 
ment of  the  views  and  in  the  collection  of  material.  Among 
others  who  have  aided  in  various  ways  in  the  development 
of  the  views  leading  up  to  the  preparation  of  this  book  and 
to  whom  thanks  are  due  are  Professors  G.  B.  Pegram  and 
H.  T.  Beans,  of  Columbia  University,  and  Dr.  Marston 
L.  Hamlin. 

NEW  YORK,  N.  Y., 
June  15,  1920. 


CONTENTS 


CHAPTER  I. 

PAGE 

INTRODUCTION;  VALENCE 1 

CHAPTER  II. 
VALENCE  (CONTINUED);  CO-ORDINATION  NUMBER 21 

CHAPTER  III. 
ACIDS  AND  BASES 41 

CHAPTER  IV. 
CATALYSIS 60 

CHAPTER  V. 

CHEMICAL  REACTIONS;  GENERAL  CONSIDERATIONS  ...     76 

CHAPTER  VI. 
SOME  CHEMICAL  REACTIONS 94 

CHAPTER  VII. 

SOME- CHEMICAL  REACTIONS  (CONTINUED) 120 

CHAPTER  VIII. 
OLEFINS  AND  THEIR  REACTION  PRODUCTS 135 

CHAPTER  IX. 
OXIDATION-REDUCTION 166 

CHAPTER  X. 
SOME  OXIDATION-REDUCTION  REACTIONS.  .  190 


IX 


CHEMICAL  REACTIONS 


CHAPTER  I. 
INTRODUCTION;    VALENCE. 

IN  order  to  classify  chemical  reactions  so  that  it  will  be 
possible  to  obtain  a  knowledge  of  the  relations  involved 
when  chemical  changes  take  place  without  considering  each 
chemical  reaction  as  an  individual  unrelated  to  any  other, 
certain  general  theories  must  be  established.  These  theories 
have  been  developed  gradually  as  the  number  and  kinds 
of  chemical  reactions  increased.  They  are  not  complete 
enough  yet  to  account  for  all  possible  changes  but  they 
serve  a  useful  purpose  and  make  possible  the  study  of 
relationships  which  would  be  obscure  without  them.  The 
general  principles  upon  which  the  theories  of  the  mechanism 
of  chemical  reactions  depend  and  which  will  be  used  here 
include  I.  The  atomic  and  molecular  theories;  II.  Valence, 
including  atomic  valence  and  the  electron  conception  of 
valence,  and  co-ordination  number;  III.  Reaction  velocity, 
especially  as  controlled  by  the  physical  conditions  and  by 
the  law  of  mass  action. 

These  principles  indicate  the  lines  which  will  be  followed 
in  the  correlation  of  chemical  reactions.  Thermodynamic 
relations  will  be  considered  only  secondarily.  Molecular 
and  atomic  chemistry,  and  in  general,  kinetic  relationships 
will  be  the  keynote  of  the  explanations  advanced.  The 
atomic  and  molecular  theories  together  with  valence  con- 
ceptions form  the  foundations.  Reaction  velocities  are  the 
important  features  in  considering  chemical  reactions  and 
the  course  these  may  take  under  given  conditions.  It  is 
impossible  to  treat  of  a  reaction  velocity  without  treating 

1 


CHEMICAL  REACTIONS. 


at  the  same  time  the  velocity  of  the  reaction  in  the  opposite 
direction,  or  in  other  words,  the  equilibrium  of  the  reaction. 
Equilibria  are  therefore  arrived  at  from  the  kinetic  and 
molecular  standpoints.  This  is  as  far  as  the  theoretical 
side  of  the  treatment  in  this  book  will  go.  It  may  be 
pointed  out  that  the  thermodynamic  treatment  reaches  the 
same  point  from  the  opposite  direction.  From  the  energy 
relationships,  deduced  from  the  laws  of  thermodynamics, 
the  equilibria  relationships  of  chemical  reactions  are  arrived 
at.  One  of  the  future  problems  of  thermodynamic  chem- 
istry is  the  development  of  reaction  velocity  relationships 
from  the  equilibria  concepts.  „ 

The  reader  of  this  book  is  supposed  to  have  completed  a 
course  in  general  inorganic  and  organic  chemistry  from  the 
modern  point  of  view.  The  relations  of  chemistry  are 
supposed  to  have  been  studied  in  such  a  way  that  the 
elementary  facts  and  phenomena  are  accurately  described, 
and  the  theories  which  develop  from  these  facts  and  phe- 
nomena applied  and  used  in  a  rational  manner.  Such  a 
study  would  include  a  portion  of  the  subject  matter  of 
what  is  very  often  taken  up  at  present  under  "physical 
chemistry." 

The  atomic  theory  is  based  upon  the  laws  of  definite  and 
multiple  proportions.  Exact  analyses  of  many  substances 
have  shown  that  the  constituent  elements  of  these  sub- 
stances are  combined  in  such  quantities  that  definite 
amounts  or  their  multiples  are  always  combined  with  each 
other.  The  atomic  theory  gives  a  definite  and  simple 
theory  to  account  for  this.  The  molecular  theory  is  based 
upon  the  existence  of  certain  quantitative  relationships 
between  the  chemical  compositions  of  substances  and  their 
relative  volumes  in  gas  form  or  osmotic  pressures  in  dilute 
solutions.  These  theories  were  based  upon  quantitative 
experimental  data  and  accounted  for  them  satisfactorily. 
In  recent  years  the  existence  of  atoms  and  molecules  has 


INTRODUCTION:  VALENCE.  3 

been  demonstrated  experimentally  so  that  no  question 
remains  as  to  their  existance.  The  reader  is  referred  to  the 
book  entitled  "The  Atom"  by  J.  Perrin  for  an  account  of 
this  work. 

The  terms  equivalent  or  combining  weight  and  formula 
weight  have  been  used  in  place  of  atoms  and  molecules  as 
not  involving  the  theories  of  atoms  and  molecules.  While 
these  terms  may  have  been  useful  at  a  time  when  the  exis- 
tence of  atoms  and  molecules  were  to  some  extent  hypo- 
thetical, the  proof  of  their  existence  in  recent  years  has 
made  the  use  of  such  terms  unnecessary. 

Following  the  atomic  and  molecular  theories,  the  study 
of  the  chemical  compositions  of  substances  led  to  the 
doctrine  of  valence  or  saturation  capacity.  Each  atom  is 
considered  to  be  capable  of  combining  with  a  definite 
number  of  atoms  of  its  own  kind  or  a  different  kind.  The 
arrangement  of  the  elements  in  the  Periodic  System  of 
Mendel eeff  brings  out  clearly  these  valence  numbers.  The 
introduction  of  dots  and  dashes  in  chemical  formulas  to 
represent  valence  linkings  forms  a  convenient  method  of 
representation. 

Sometimes  confusion  has  been  caused  by  taking  valence 
linkings  to  represent  some  form  of  combining  power  or 
stability.  This  question  must  be  made  clear  and  the  mean- 
ing of  valence  defined  carefully  for  a  proper  understanding 
of  the  questions  to  be  taken  up.  In  order  to  do  this, 
chemical  energy  will  be  taken  up  for  a  moment  and  the 
relation  between  it  and  valence  described. 

For  some  purposes,  it  has  been  considered  that  energy 
might  be  assumed  to  be  the  product  of  two  factors,  an 
"intensity"  factor  and  a  " capacity"  factor.  For  example, 
in  mechanical  work  or  energy,  in  which  the  work  is  taken 
to  be  equal  to  the  product  of  force  into  distance,  the  force 
would  be  the  intensity  factor  and  the  distance  the  capacity 
factor.  This  division  of  energy  into  factors  is  entirely 


4  CHEMICAL  REACTIONS. 

arbitrary.  It  serves  a  useful  purpose  in  certain  cases,  but 
its  limitations  must  be  remembered.  The  intensity  and 
capacity  factors  of  mechanical  energy  need  bear  no  relation 
except  in  name,  to  the  intensity  and  capacity  factors  of 
electrical  energy  or  of  chemical  energy  or  of  any  other  form 
of  energy.  For  each  form  of  energy  a  different  division 
may  be  made.  This  can  be  shown  most  directly  by  express- 
ing the  two  factors  of  some  of  the  different  forms  of  energy 
in  terms  of  the  C.G.S.  system  of  length  (L),  mass  (M),  and 
time  (T)  units.  The  dimensions  of  energy  are  always  given 
by  the  expression  ML2T~2.  In  energy  considered  as  me- 
chanical work,  force  may  be  called  the  intensity  factor  and 
is  given  by  the  product  of  mass  times  acceleration  or  MLT~2, 
and  the  displacement  the  capacity  factor  equal  to  L.  In 
electrical  energy,  for  an  electrostatic  current,  the  electro- 
motive force  may  be  called  the  intensity  factor  and  is  given 
by  the  expression  Mll2Ll>2T~l,  and  the  electricity  or  charge 
or  coulombs  the  capacity  factor  and  given  by  the  expression 
Mll2Lll>2T-1.  These  two  sets  of  factors  show  the  usual 
way  of  yiewing  the  intensity  and  capacity  factors  of  these 
two  forms  of  energy.  For  chemical  energy,  still  another 
way  of  viewing  the  possible  energy  relations  is  customary. 
Here,  the  intensity  factor  may  be  considered  to  be  given 
by  the  change  of  free  energy  of  the  reaction  under  certain 
definite  conditions  to  be  formulated  presently.  This  is  the 
chemical  affinity,  and  the  units  in  which  it  is  expressed 
given  by  ML2T~2.  Obviously  then,  the  capacity  factor  of 
chemical  energy  would  be  a  number.  This  numerical 
capacity  corresponds  to  what  is  known  as  valence. 

This  brief  statement  required  further  explanation,  how- 
ever. If  the  change  in  free  energy  is  referred  to  the  com- 
bination taking  place  between  equivalent  weights  of  chem- 
ical substances,  that  is  to  say,  between  the  unit  weights  of 
chemical  combination,  then,  when  considering  molecules 
or  formula  weights,  the  numbers  of  equivalents  taking 


INTRODUCTION:  VALENCE.  5 

part  would  indicate  the  capacity  factor  or  valence.  Valence 
is  therefore  represented  as  a  number  and  the  product  of 
change  in  free  energy  per  equivalent  and  valence  represents 
the  change  in  free  energy  in  the  formation  of  the  substance 
in  the  molecular  state.  In  ferrous  chloride,  for  example, 
the  free  energy  or  chemical  affinity  of  the  two  chlorine 
atoms  in  combination  with  the  iron  may  be  assumed  to  be 
the  same;  in  ferric  chloride,  similarly,  that  of  each  of  the 
three  chlorine  atoms  may  be  assumed  to  be  equal,  but  not 
necessarily  the  same  as  for  the  chlorine  atoms  in  ferrous 
chloride.  The  difficulty,  if  not  impossibility  of  determining 
the  free  energy  change  when  two  atoms  of  a  more  complex 
molecule  combine,  makes  it  necessary  in  practice  to  speak 
only  of  the  change  in  free  energy  in  the  formation  of  a 
compound  and  not  of  the  separate  combinations  between 
pairs  of  atoms  in  the  compound. 

Keeping  in  mind  the  significance  of  the  terms  intensity 
and  capacity  factors,  they  will  now  be  used  in  discussing 
chemical  energy  as  they  form  a  convenient  method  for 
presenting  certain  definite  relationships.  The  chemical 
energy  contained  in  a  given  compound  having  a  definite 
molecular  formula  involves  the  number  of  atoms  in  the 
molecule  and  the  affinity  with  which  these  atoms  are  com- 
bined with  each  other.  The  chemical  affinity  involved  in 
a  compound  is  a  definite  quantity.  It  is  given  numerically 
as  the  value  of  the  affinity  of  that  compound  compared  to 
the  value  of  the  affinity  of  the  substances  from  which  it 
is  formed.  That  is  to  say,  the  chemical  affinity  of  a  com- 
pound is  given  as  a  difference,  not  as  an  absolute  value. 
It  may  be  measured  in  any  of  the  ordinary  units  of  energy, 
and  represents  the  external  work  which  may  .be  obtained 
when  the  substance  is  formed  from  its  component  parts  by 
a  reversible  isothermal  reaction.  This  external  work  is 
generally  known  as  the  change  in  free  energy  in  the  forma- 
tion of  the  compound  and  is  the  true  measure  of  the  change 


6  CHEMICAL  REACTIONS. 

in  the  chemical  affinity.  The  actual  measurements  of 
these  values  may  be  carried  out  in  several  ways.  A  direct 
method  involves  the  electromotive  force  measurements  of 
a  reversible  cell  under  definite  conditions.  A  more  general 
method  is  the  determination  of  the  equilibrium  constants 
of  definite  reactions.  At  the  present  time  very  few  organic 
reactions  are  available  for  the  former  method,  while  for 
the  latter,  the  accurate  determinations  of  a  large  number  of 
equilibria  in  organic  reactions  have  not  been  carried  out. 
There  are,  consequently,  comparatively  few  data  at  hand 
to  enable  the  exact  relative  thermodynamic  stabilities  of 
organic  compounds  to  be  calculated.  It  is  very  desirable 
that  such  determinations  be  made,  as  they  represent  one 
of  the  most  important  problems  in  chemistry  at  the  present 
time.  Such  values  would  give  a  true  measure  of  the  rela- 
tive stabilities  of  compounds,  or  the  magnitude  of  the 
chemical  affinities.  Many  organic  chemists  have  been  in 
the  habit  of  speaking  of  the  stability  of  a  compound  when 
the  rate  at  which  the  compound  reacted  was  meant.  Re- 
action velocities  bear  no  simple  relation  to  the  stability  or 
affinity,  and  deductions  with  regard  to  the  affinity  with 
which  two  atoms  are  combined,  simply  on  the  basis  of  the 
rate  with  which  they  react  with  other  substances,  are  wrong 
in  principle  and  fact. 

The  terms  upon  which  the  intensity  factor  of  chemical 
energy  or  the  chemical  affinity  depend  may  be  indicated 
as  follows:  Every  reaction  is  (thermodynamically)  rever- 
sible. The  greater  the  affinity  which  causes  two  substances 
to  combine  or  react,  the  greater  will  be  the  proportion  or 
amounts  of  the  products  formed,  and  the  more  difficult 
will  it  be  to  decompose  the  products.  The  chemical  affinity 
will  consequently  be  greater,  the  more  the  equilibrium  lies 
in  the  direction  of  the  formation  of  the  products;  or,  in 
other  words,  the  value  of  the  chemical  affinity  is  connected 
with,  or  may  be  calculated  from  some  function  of  the 


INTRODUCTION:  VALENCE.  7 

equilibrium  constant.     Van't  Hoff,  in  1883,  showed  this 
function  to  be  given  by  the  equation 

(1)  A  =  RT  log,  K  -  RT  log, 


for  a  chemical  reaction  represented  by  the  equation 

(2)  naM  +nbN+  ...  =  n'a'M'  +  n'b>N'+ 

in  which  A  represents  the  change  in  free  energy  or  the 
chemical  affinity  of  the  reaction  (2);  R,  the  gas  constant; 
T,  the  absolute  temperature  at  which  the  reaction  takes 
place;  K,  the  equilibrium  constant  of  the  reaction  repre- 
sented by  equation  (2)  ;  and  the  different  values  of  C  in 
the  second  term  of  the  right-hand  side  of  equation  (1) 
the  concentrations  of  the  reacting  substances  of  equation 
(2).  If  these  concentrations  are  chosen  as  equal  to  unity, 
the  chemical  affinity  is  found  to  be 

(3)  A  =  RTlogeK. 

The  relation  between  the  equilibrium  constant,  K,  of  a 
reaction,  and  the  heat,  of  the  reaction  at  constant  volume  Q, 
both  at  the  absolute  temperature  T7,  was  shown  by  Van't 
Hoff  to  be 

m  dlogeK  _Q_ 

dT  RT*' 

The  following  equation,  (5),  is  known  as  the  Gibbs-Helm- 
holtz  equation. 


This  shows  the  relation  between  the  change  in  free  energy, 
or  the  chemical  affinity  of  a  reaction,  the  heat  of  reaction 
at  constant  volume,  the  absolute  temperature  at  which 
the  reaction  proceeds,  and  the  temperature  coefficient  of 
the  chemical  affinity,  dA/dT,  of  the  reaction.  These  three 


8  CHEMICAL  REACTIONS. 

equations  are  fundamental  for  the  relations  between  the 
chemical  affinity  of  a  reaction  and  other  physical  and 
chemical  quantities. 

The  last  equation  shows  that  only  if  T  =  0  or  if 
dAjdT  —  0  is  the  heat  of  reaction  equal  to  the  chemical 
affinity.  The  equality  of  these  two  is  therefore  only  a 
special  case,  and  as  T  increases,  they  are  likely  to  diverge 
more  and  more.  Whether  the  heat  of  reaction  is  greater 
or  less  than  the  chemical  affinity  will  depend  upon  whether 
the  change  in  the  chemical  affinity  with  the  temperature  is 
negative  or  positive.  In  equation  (5)  the  electromotive 
force  of  a  reversible  cell  per  gram-equivalent  of  substance 
transformed  (since  one  faraday  of  electricity  is  associated 
with  one  gram  equivalent  of  substance)  may  be  substituted 
for  A,  since  it  is  a  measure  of  the  change  of  free  energy  of 
the  chemical  reaction  taking  place  in  such  a  cell. 

The  capacity  factor  of  chemical  energy  may  be  considered 
to  be  valence.  Valence  is  a  number,  and  is  a  distinct  factor 
not  involving  chemical  affinity.  For  reasons  which  have 
already  been  given,  the  chemical  affinities  of  organic  com- 
pounds have  been  determined  only  in  isolated  cases.  On 
the  other  hand,  valence  has  been  a  valuable  aid  in  classifying 
the  compounds  of  organic  chemistry,  so  that  it  is  the  latter 
which  has  been  used  to  the  greater  extent  in  that  field. 
At  the  same  time  another  reason  for  this  may  be  given. 
The  change  in  free  energy,  or  the  thermodynamic  stability, 
while  of  the  greatest  importance,  has  nothing  to  do  with 
the  time  factor.  That  is  to  say,  it  gives  the  stability  of  a 
compound  when  equilibrium  has  been  reached.  Now  the 
element  carbon  often  shows  great  inertia  or  chemical  re- 
sistance in  many  of  its  compounds  and  reactions.  The 
velocity  with  which  it  enters  into  reactions  is  often  very 
small  even  though  the  free  energy  involved  in  the  chemical 
change  is  very  great.  As  a  result,  compounds  of  carbon 
are  known  which  have  no  thermodynamic  right  to  exist, 


INTRODUCTION:  VALENCE.  9 

that  is  to  say,  if  equilibrium  were  attained,  none  or  only 
infinitesimal  amounts  of  the  substances  would  be  present. 
The  rate  of  reaction  is  so  small,  however,  that  equilibrium 
ordinarily  is  not  attained,  and  therefore  organic  chemistry 
has  very  often  to  deal  with  these  (thermodynamically) 
unstable  substances.  While,  therefore,  undoubtedly,  the 
affinity  relationships  of  organic  compounds  will  ultimately 
be  of  predominant  importance,  until  more  is  known  of 
these,  valence,  which  is  not  affected  by  the  time  factor  in 
this  way,  has  had  to  serve  as  the  classifying  principle. 
But  in  using  valence  in  this  way  it  is  not  permissible  to 
introduce  exact  measures  of  the  comparative  stabilities  as 
has  been  attempted  so  often,  as  already  pointed  out.  All 
that  can  be  done  as  a  result  of  the  comparative  study  of 
large  numbers  of  compounds  is  to  say  which  would  probably 
exist  under  ordinary  conditions  and  whether  some  would 
react  more  rapidly  than  others.  These  qualitative  factors 
do  not  give  any  information  concerning  the  real  quantitative 
measures  of  relative  stability. 

A  single  linking  between  two  atoms  gives  no  information 
as  to  the  stability  of  the  union  between  these  atoms.  A 
double  linking  between  two  atoms  cannot  give  any  more 
information  with  regard  to  the  stability  of  the  union. 
Qualitatively,  it  has  been  found  that  the  rate  of  reaction 
for  compounds  containing  double  linkings  is  greater  in  some 
ways  than  the  rate  for  compounds  containing  single  linkings, 
and  that  with  certain  reagents,  decomposition  at  the  double 
linking  occurs  more  rapidly  than  at  other  parts  of  the 
molecule,  but  this  is  manifestly  different  from  a  discussion 
of  true  stabilities  of  compounds.  The  double  linking  in 
the  ordinary  language  signifies  two  units  of  valence  just 
as  the  single  linking  denotes  one  unit  of  valence,  and  in  this 
sense,  the  only  permissible  one,  the  representation  of  a 
double  linking  by  two  lines  or  dashes  is  a  correct  picture 
of  the  union  when  one  line  is  used  for  the  single  linking. 


10  CHEMICAL  REACTIONS. 

These  valence  views  may  now  be  carried  further  and  the 
later  conceptions  involving  the  electrons  and  the  electron 
conception  of  valence  described.  These  developments  did 
not  take  place  suddenly  but  occurred  gradually  as  new 
experimental  work  showed  that  the  older  views  were  not 
sufficient  to  include  all  the  facts  known.  For  instance, 
oxides  are  at  times  spoken  of  as  acid  oxides  and  basic  oxides. 
Electrolytic  studies  on  the  decomposition  of  salts  and  other 
substances  in  solution  indicate  a  real  difference  between 
the  two  parts  of  the  molecules.  The  distinction  may  be 
carried  further  and  acid-forming  elements  and  base-forming 
elements  designated,  as  brought  out,  for  instance,  by  the 
oxides  of  the  elements  of  the  different  groups  in  the  Periodic 
System.  The  names  non-metals  and  metals  may  be  taken 
to  be  practically  synonymous  with  acid-forming  and  base- 
forming  elements,  and  finally  these  may  be  used  inter- 
changeably with  electronegative  and  electropositive  ele- 
ments. This  development  of  terminology  leads  to  the 
following  definition  or  description  of  valence :  The  valence 
of  an  element  is  equal  to  the  number  of  equivalents  of  the 
acidic  or  of  the  basic  constituents  combined  with  or 
associated  with  one  formula  weight  of  that  element. 
Arrhenius's  theory  of  ionization  has  shown  that  certain 
of  the  atoms  or  groups  actually  do  carry  electric  charges, 
and  has  fixed  the  terms  electropositive  and  electronegative 
as  having  a  readily  demonstrable  existence  with  these 
substances. 

J.  J.  Thomson,  in  1904,  put  forward  as  a  possible  develop- 
ment a  new  view  of  valence.  Instead  of  quoting  the  brief 
presentation  given  by.  him,  an  attempt  will  be  made  to 
develop  the  subject  more  completely.  If  a  solution  of 
ferrous  chloride  is  placed  in  beaker  A,  and  a  solution  of 
potassium  permanganate  in  beaker  B,  the  two  solutions 
connected  by  a  salt  bridge  C  containing  a  solution  of  some 
neutral  salt  dipping  into  both  solutions,  and  by  a  wire  with 


INTRODUCTION:  VALENCE.  11 

a  galvanometer  in  circuit  connecting  the  two  electrodes  D 
and  D'  which  dip  into  the  solutions,  it  will  be  noticed  that 
a  positive  current  will  flow  in  the  direction  B  to  A  in  the 
wire.  If  the  contents  of  beaker  A  be  examined  now,  it 
will  be  seen  that  the  iron  has  been  oxidized  to  the  ferric 
form.  If  the  amount  of  positive  electricity  flowing  through 
the  circuit  from  B  to  A  were  measured  and  the  amount  of 
ferrous  iron  changed  into  ferric  iron  were  also  measured, 
it  would  be  found  that  for  every  formula  weight,  or  mol,  of 
ferrous  iron  changed  into  ferric  iron,  96,500  coulombs  of 
electricity  had  passed  through  the  circuit.  Therefore  it 
may  be  said  that  one  mol  of  ferrous  iron  differs  from  one 
mol  of  ferric  iron  by  96,500  coulombs.  In  this  way  it  may 
be  brought  out  that 

One  mol  of  iron  =  56  grams  of  iron. 
"      "     "  ferrous  iron  =  56  grams  of  iron— 2  X  96,500 

coulombs  negative  electricity. 
"      "     "  ferric    iron  =  56    grams    of    iron— 3  X  96,500 

coulombs  negative  electricity. 

From  these  values  it  is  evident  that  the  amount  of  positive 
electricity  associated  with  the  mol  of  iron  corresponds  to 
the  number  of  mols  of  atomic  chlorine  that  the  mol  of  iron 
can  hold  in  chemical  union,  or,  in  other  words,  there  is  a 
definite  relation  between  the  amount  of  electricity  and  the 
valence  of  the  iron. 

If,  instead  of  a  solution  of  ferrous  chloride,  an  alkaline 
solution  of  formaldehyde  is  placed  ^^ 

in  beaker  A,  it  will  be  found  that  o^^-^-O        D1 

again  a  positive  current  will  flow 
from  B  to  A,  in  the  wire,  and  if 
the  constants  of  beaker  A  are  ex- 
amined, it  will  be  noticed  that  the 
formaldehyde  has  been  changed 
into  formic  acid,  or  oxidation  has  taken  place.  The  amount 


12  CHEMICAL  REACTIONS. 

of  current  passed  through  the  circuit  when  compared  to  the 
number  of  mols  oxidized  is  not  as  readily  measured  as  with 
the  former  experiment,  but  this  experiment  shows  that 
oxidation,  and  therefore  reduction,  with  organic  compounds 
as  with  inorganic  compounds  is  accompanied  by  electrical 
changes. 

If  the  amount  of  electricity  in  any  oxidation-reduction 
reaction  involving  electrolytes  be  measured,  it  will  be  found 
that,  for  every  mol  of  an  element  undergoing  oxidation  or 
reduction,  96,500  coulombs  or-  a  simple  multiple  of  this 
quantity,  are  always  involved.  Similarly,  if  the  charge, 
either  positive  or  negative,  carried  by  one  mol  of  any  ion  in 
a  solution  be  measured,  it  will  also  be  found  to  be  96,500 
coulombs  or  a  simple  multiple  of  this  quantity.  The  quan- 
tity of  electricity  in  all  of  these  reactions  appears  to  obey 
a  law  of  definite  and  multiple  proportions.  Just  as  the 
atomic  theory  of  matter  is  based  upon  these  laws,  so 
electricity  may  be  regarded  as  atomic  in  character,  and 
96,500  coulombs  represents  one  combining  unit,  or  if  the 
expression  may  be  used,  one  combining  weight  of  elec- 
tricity. The  smallest  quantity  of  electricity  associated  with 
one  atom  of  matter  is  generally  known  as  an  electron. 
The  existence  of  the  electron  has  been  proven  by  the  work 
of  a  number  of  physicists,  especially  by  J.  J.  Thomson  and 
R.  A.  Millikan. 

Taking  into  consideration  the  definition  of  valence  given 
before  and  the  experiments  and  conclusions  therefrom  just 
described,  it  is  now  possible  to  give  a  general  definition  of 
valence  which  may  be  applied  readily  and  used  as  simply 
as  the  older  definition  of  valence.  The  valence  of  an  element 
may  be  defined  as  the  number  of  negative  electrons  an  atom  of 
that  element  loses  or  gains  to  form  chemical  Unkings.  In 
accordance  with  the  modern  developments  of  physics,  the 
negative  electron  (or  corpuscle)  is  accepted  as  a  unit  (or 
atom)  of  electricity.  This  view  of  valence  states  that 


INTRODUCTION:  VALENCE.  13 

every  chemical  linking  between  two  atoms  involves  the 
transfer  of  a  negative  electron  from  one  atom  to  the  other. 
This  transfer  of  a  negative  electron  requires,  assuming  the 
atom  itself  to  be  electrically  neutral,  that  the  atom  which 
loses  the  electron  acquires  a  unit  positive  charge,  the  atom 
which  gains  the  electron,  a  unit  negative  charge. 

The  question  now  naturally  arises:  How  is  it  possible  to 
ascertain  which  atom  is  positive  and  which  is  negative  in  a 
compound?  For  substances  which  conduct  the  current  in 
solution,  the  charges  manifested  by  some  of  the  atoms  or 
groups  of  atoms  will  show  directly  the  distribution  of  some 
of  these  electric  charges.  In  general,  the  relative  positions 
of  the  elements  in  the  Periodic  System,  which  is  itself  an 
expression  of  the  chemical  properties  of  the  elements,  serves 
as  a  guide  in  determining  this  point.  In  the  horizontal 
rows,  the  elements  of  larger  atomic  weights  are  usually 

negative  to  those  of  smaller  atomic  weights;   thus,  NaCl; 

=  +       =  +       #  - 

NH3;    CH4;    CCU;    etc.     In  the  vertical  series  the  main 

and  subgroups  must  be  considered  separately. 

The  older  terms,  positive  and  negative  elements,  now 
acquire  a  more  precise  meaning.  A  positive  element  is 
one,  whose  atom,  in  chemical  combination,  has  lost  one  or 
more  negative  electrons;  a  negative  element,  one  whose 
atom  in  chemical  combination  has  gained  one  or  more 
electrons.  When  an  atom  is  reduced,  it  gains  negative  or 
loses  positive  charges.  Since,  in  any  given  compound,  the 
atom  which  acquires  the  electron  is  the  one  which  has  the 
greater  attraction  for  it  under  the  given  conditions,  and 
since  the  loss  or  gain  of  an  electron  signifies  that  the  element 
is  either  oxidized  or  reduced,  the  following  generalization 
may  be  stated :  That  element  in  a  compound  is  the  positive 
element,  which  shows  the  smaller  oxidizing  or  greater  reduc- 
ing potential  (or  has  the  smaller  attraction  or  affinity  for 
the  negative  electron) ;  and  conversely,  that  element  which 


14  CHEMICAL  REACTIONS. 

has  the  greater  oxidizing  potential  (or  the  greater  affinity 
for  the  negative  electron)  is  the  negative  element.  This 
generalization  substitutes  the  affinity  of  the  elements  for 
the  electrons  for  the  affinity  of  the  elements  toward  each 
other  as  was  done  formerly.  The  relative  oxidizing  poten- 
tials signify  the  same  relations  as  the  chemical  affinity  of 
different  atoms  for  each  other.  Just  as  with  the  other 
measures  of  the  intensity  factor  of  chemical  energy,  the 
use  of  the  oxidizing  potential  must  for  the  present  be  limited 
to  qualitative  relations  with  most  organic  substances. 

It  is  possible  to  conceive  of  compounds  in  which  the  two 
elements  which  enter  into  chemical  combination  have  oxi- 
dizing potentials  so  close  to  each  other  in  value  that  two 
combinations  are  possible  in  which  the  positive  and  negative 
elements  are  interchanged  in  the  two  compounds.  As  an 
example  of  this  type  of  isomerism,  the  two  isomeric  iodine 
chlorides  may  be  mentioned.  Since  chlorine  has  the  higher 
oxidizing  potential,  it  is  highly  probable  that  in  the  more 
stable  of  the  two  isomers  the  iodine  atom  is  positive,  while 
in  the  less  stable,  the  chlorine  is  positive.  The  formulas 

for  the  two  compounds  may  be  written  IC1  for  the  stable 

+  — 

form,  and  C1I  for  the  unstable  form.  When  the  oxidizing 
potentials  of  the  elements  differ  very  much  in  value,  iso- 
merism of  this  form  would  not  be  so  likely.  Thus  with 
hydrogen  chloride,  the  form  HC1  would  very  likely  be  so 
unstable  that  it  would  be  impossible  for  it  to  exist  under 
ordinary  conditions,  and  it  would  therefore  be  unknown. 
It  has  often  been  observed  that  the  conditions,  such  as  the 
presence  of  other  substances,  influence  the  oxidizing  poten- 
tials of  the  elements  or,  as  formerly  expressed,  the  affinity 
pf  the  elements  for  each  other.  Likewise,  the  pressure  and 
temperature  of  a  mixture  of  methane  and  water  may  be 
such  that  the  negative  carbon  of  the  methane  is  oxidized 
to  the  positive  carbon  of  carbon  monoxide  or  dioxide.  It, 
therefore,  seenjs  possible  that  differences  in  conditions  may 


INTRODUCTION:  VALENCE.  15 

also  give  rise  to  electroisomers.  Moreover,  for  many  com- 
pounds of  carbon  in  which  several  atoms  of  carbon  are 
joined  with  each  other,  it  is  often  very  difficult  to  know 
which  of  the  carbon  atoms  is  positive. 

It  may  also  be  repeated  that  the  chemical  resistance  or 
the  inertia  of  carbon  compounds  may  also  give  rise  to 
electroisomers,  since  one  of  the  isomers  while  very  unstable 
may  still  exist  due  to  its  extremely  slow  rate  of  decomposi- 
tion. 

The  theory  of  electric  dissociation  of  Arrhenius  showed 
that  the  ions  in  solution  carried  definite  charges.  The 
number  of  these  charges,  taken  in  connection  with  the 
general  views  of  positive  and  negative  elements,  and  acidic 
and  basic  constituents  of  compounds,  were  found  to  be 
identical  with  the  valence  numbers  of  these  atoms  and 
groups.  In  this  way  arose  the  one  direct  experimental 
method  of  determining  valence;  the  measurement  of  the 
electric  charges  on  the  ions.  This  method  is  of  limited 
application,  however,  since  many  substances  are  not  ionized 
in  solution,  and  this  gave  rise  to  the  view  that  if  a  substance 
did  not  ionize,  its  atoms  were  not  united  in  the  same  way 
as  the  atoms  of  a  substance  which  did  ionize.  The  possible 
action  of  the  solvent  was  not  considered  in  this  connection. 
Two  kinds  of  valence  were,  therefore,  adopted  by  a  number 
of  chemists,  polar  valence  and  non-polar  valence.  Since 
inorganic  compounds,  mainly,  are  ionized  in  solution,  and 
organic  compounds  not  ionized,  this  division  was  roughly 
applied  in  such  a  way  that  inorganic  compounds  were 
assumed  to  contain  polar  valences,  and  organic  compounds, 
non-polar  valences. 

There  are  a  number  of  arguments  against  the  assumption 
of  two  kinds  of  combining  forces  in  place  of  one  kind  (polar). 
The  untenability  of  the  dual  view  may  be  seen  most  readily 
with  some  of  the  phenomena  of  oxidation  and  reduction. 

As  already  stated,  the  correct  definition  for  oxidation  and 


16  CHEMICAL  REACTIONS. 

reduction  with  inorganic  compounds,  as  generally  accepted, 
is  unquestionably  that  involving  a  change  in  the  electrical 
charges  of  the  atoms;  for  oxidation,  gain  of  positive  charges, 
or  loss  of  negative  charges,  for  reduction,  the  reverse. 

In  the  explanation  of  oxidation-reduction  involving  the 
transfer  of  electrons,  it  becomes  evident  that  in  speaking 
of  oxidation-reduction  it  would  be  more  correct  to  say  that 
a  particular  element  in  a  compound  is  oxidized  or  reduced. 
Thus  in  the  case  of  the  oxidation  involved  in  changing 
ferrous  chloride  into  ferric  chloride,  it  is  the  iron  which  is 
oxidized,  the  chlorine  is  neither  oxidized  nor  reduced. 
Because  of  the  incorrent  way  of  saymg  that  a  compound 
has  been  oxidized  or  reduced,  the  meaning  of  the  terms 
oxidation  and  reduction  has  in  many  instances  become 
vague.  If  electrons  are  not  responsible  for  the  union  be- 
tween atoms  in  molecules  which  are  not  electrolytes,  the 
electrical  definition  of  oxidation  and  reduction  becomes 
inapplicable  and  it  is  necessary  either  to  fall  back  upon  some 
of  the  older  definitions  or  to  use  an  entirely  new  one  for 
these  cases.  So  far  no  new  definition  has  been  proposed, 
and  the  older  definitions  are  still  used  in  organic  chemistry. 
Thus  the  addition  of  oxygen,  or  the  removal  of  hydrogen, 
is  taken  to  be  the  common  characteristic  for  an  oxidation. 
To  illustrate  this  point:  The  conversion  of  methane  into 
carbon  dioxide  and  water  by  means  of  oxygen,  would  be 
considered  oxidation,  according  to  the  older  definitions. 
Methane  can  also  be  converted  into  carbon  dioxide  by 
treatment  with  chlorine,  that  is  substitution,  and  sub- 
sequent hydrolysis,  neither  action  being  oxidation  according 
to  the  older  definition.  Many  other  examples  might  be 
mentioned,  and  the  general  conclusion  is  arrived  at,  that 
it  would  be  impossible  to  give  any  satisfactory  definition  of 
oxidation  applicable  to  all  cases.  Furthermore,  the  oxida- 
tion of  formaldehyde  by  permanganate  as  described  before 
showed  that  the  oxygen  from  the  permanganate  did  not 


INTRODUCTION:  VALENCE,  17 

add  to  the  formaldehyde  since  the  permanganate  was  not 
in  the  same  beaker.  There  was  a  current  of  negative  elec- 
tricity flowing  from  the  formaldehyde  solution  to  the 
permanganate  solution.  A  similar  experiment  may  be 
carried  out  with  ethyl  alcohol  in  place  of  the  formaldehyde. 
The  formaldehyde  and  ethyl  alcohol  belong  to  the  class  of 
non-electrolytes,  and  unless  the  union  between  the  atoms 
is  considered  polar  in  character,  it  would  be  very  difficult 
to  find  a  suitable  definition  or  description  for  this  form  of 
oxidation. 

Since  the  experimental  evidence  at  hand  is  no  more 
against  than  in  favor  of  the  view  that  electrons  are  respon- 
sible for  valence  in  the  case  of  non-electrolytes  than  in  the 
case  of  electrolytes,  while  indirect  evidence  is  in  favor  of 
this  view,  it  is  much  simpler  to  adopt  the  view  of  one  kind 
of  force  acting  between  atoms  in  all  compounds,  that  is, 
that  due  to  the  electron  associated  with  the  atom.  This 
at  once  furnishes  one  definition  for  all  oxidation-reduction 
reactions  applicable  to  all  cases  and  easily  understood. 

A  few  words  regarding  the  application  of  valence  may 
be  of  value  here.  Valence  is  a  number.  Experimental 
facts  have  made  the  negative  electron  (the  atom  of  elec- 
tricity) the  basis  on  which  to  build.  From  the  chemical 
side,  the  valence  of  an  atom  shows  the  number  of  atoms  (or 
groups  of  atoms)  held  in  combination  by  that  atom  when 
the  hydrogen  atom  as  it  exists  in  most  of  its  compounds  is 
taken  as  the  positive  unit  (loss  of  one  negative  electron). 
These  relations  of  positive  and  negative  make  it  clear 
that  in  speaking  of  valence,  it  is  not  sufficient  to  give  a 
number  for  its  value,  but  that  at  the  same  time  it  must  be 
stated  whether  the  number  is  positive  or  negative,  that  is 
to  say,  whether  negative  electrons  have  been  lost  or  gained 
in  the  combination  of  the  atom  in  question.  This  has 
evidently  developed  as  a  matter  of  practical  expediency 
from  the  experimental  evidence  upon  which  the  theory  of 


18  CHEMICAL  REACTIONS. 

valence  is  based.  It  would  be  possible  to  construct  a 
theory  of  valence  using  as  the  basis  the  atoms  of  the 
elements  which  have  gained  the  greatest  number  of  negative 
electrons  among  all  the  elements  in  the  formation  of  chem- 
ical linkings,  and  to  consider  all  other  combinations  as 
positive  valences.  This  treatment  would  simply  amount  to 
a  shift  of  the  standard  of  reference  from  what  is  now  con- 
sidered to  be  an  electrically  neutral  atom,  to  an  atom 
carrying  the  maximum  number  of  negative  charges  (which 
is  eight),  and  to  consider  the  valence  as  positive  when 
compared  with  this  new  zero  standard.  This  method  of 
treatment  would  obscure  somewhat  the  relative  positive 
and  negative  relations  of  the  elements,  which  have  been 
developed  as  the  result  of  experience.  At  any  rate,  while 
it  is  important  to  point  out  that  the  standard  or  basis  in 
use  is  arbitrary  in  the  sense  that  it  is  based  upon  experi- 
mental facts  which  were  obtained  without  reference  to 
any  theory  of  valence,  in  order  to  retain  the  connection 
between  the  theory  of  valence  and  other  fields  of  science, 
the  standard  evolved  will  be  adhered  to  strictly  in  the 
further  developments. 

Earlier  in  this  chapter  it  was  pointed  out  that  change  in 
free  energy  per  unit  (equivalent)  weight  multiplied  by 
valence  would  give  the  change  in  free  energy  per  molecule 
in  the  formation  of  the  substance  in  question.  In  using 
valence  in  this  way,  the  electropositive  or  electronegative 
character  of  the  atom  would  not  be  included  in  determining 
the  change  in  free  energy  of  the  molecule,  since  the  positive 
or  negative  sign  of  this  free  energy  change  depends  upon 
other  factors  and  comparative  units  used  and  the  method 
of  calculating  these  values  as  developed  historically.  This 
statement  is  made  to  avoid  confusion  in  the  use  of  valence 
as  a  number  (not  positive  or  negative)  in  free  energy  calcula- 
tions, and  valence  (relative  positive  and  negative  states  of 
the  atoms)  in  connection  with  the  electron  conception  of 
valence. 


INTRODUCTION:  VALENCE.  19 

~  + 
Nitrogen  in  ammonia  has  a   valence  of   —  3,    (NH3). 

-f p 

Nitrogen  in  nitrous  acid  has  a  valence  of  +  3,  (HO  N  O). 
Nitrogen  in  ammonia  therefore  differs  from  nitrogen  in 
nitrous  acid  by  six  units  of  valence.  The  great  difference 
in  the  properties  of  the  nitrogen  in  the  two  compounds  is  an 
expression  of  the  difference  in  valence.  (On  the  former 
non-polar  view  of  valence,  nitrogen  was  considered  to  have 
a  valence  of  3  in  both  compounds.)  Nitrogen  in  nitric 
acid  has  a  valence  of  +  5.  The  difference  between  the 
nitrogen  in  the  extreme  states  is  eight  units  of  valence. 
Oxidation  of  an  atom  consists  in  the  loss  of  negative  charges 
or  the  gain  of  positive  charges,  and  therefore  the  change  of 
nitrogen  in  ammonia  to  the  nitrogen  in  nitric  acid  consists 
of  an  oxidation  of  eight  units.  The  other  atoms  combined 
with  the  nitrogen  in  these  compounds  do  not  change  their 
charges,  or  are  neither  oxidized  nor  reduced,  oxygen  having 
a  valence  of  —  2  and  hydrogen  a  valence  of  +  1  in  all  three. 

The  compounds  of  carbon  show  similar  relationships. 

— —  + 
Carbon  in  methane  has  a  valence  of  —  4  (C  H4) .     Carbon 

4-  4- 
+  4-    - 

in  carbon  tetrachloride  'has  a  valence  of  +  4  (C  CU) .  The 
difference  in  the  valence  of  the  carbon  in  the  two  com- 
pounds is  eight  units,  or  the  carbon  in  carbon  tetrachloride 
is  in  a  state  of  oxidation  eight  units  greater  than  that  of 

the  carbon  in  methane.  In  methyl  chloride  (C  H3C1),  the 
carbon  atom  has  lost  one  negative  electron  and  gained 
three,  or  its  valence  is  —  3  +  1,  and  its  state  of  oxidation 

—  2;    in   dichlormethane,   the   valence   of   the   carbon   is 

—  2+2  and  its  state  of  oxidation  0;   in  chloroform,  the 
valence  of  the  carbon  is  —  1  +  3  and  its  state  of  oxidation 
+  2.     This  series  of  compounds  shows  the  importance  of 
stating  in  full  the  charges  of  the  atoms  which  go  to  make 
up  the  valence,  and  it  also  illustrates  the  meaning  of  the 
term  oxidation  of  an  atom.     The  state  of  oxidation  of  an 


20  CHEMICAL  REACTIONS. 

atom  conveys  a  definite  meaning  chemically  only  in  com- 
parison with  the  atom  in  the  other  states  of  oxidation. 
The  change  in  the  valence  of  the  atom  is  the  significant 
fact  in  speaking  of  oxidation,  and  while  the  state  of  oxida- 
tion may  be  shown  by  the  number  and  sign  of  its  valence, 
its  importance  is  only  clear  and  definite  in  comparison  with 
other  states  of  oxidation  of  the  same  atom. 

In  general  terms,  the  extreme  difference  which  an  atom 
shows  in  its  valence  is  eight  units;  for  example,  chlorine  in 
hydrogen  chloride  (—1)  and  chlorine  in  perchloric  acid 
(+  7);  sulfur  in  hydrogen  sulfide  (—2)  and  sulfur  in 
sulfuric  acid  (+  6);  nitrogen  in  ammonia  (—3)  and  nitro- 
gen in  nitric  acid  (+  5);  carbon  in  methane  (—4)  and 
carbon  in  carbon  tetrachloride  (+  4) .  This  difference 
refers  to  the  same  relation  to  which  Mendeleeff  referred  in 
his  Periodic  System  when  he  stated  that  the  sum  of  the 
valences  toward  oxygen  and  toward  hydrogen  of  the  ele- 
ments of  the  V,  VI,  and  VII  Groups  was  equal  to  eight. 
The  compounds  of  the  elements  of  the  I,  II,  and  III  Groups 
in  which  they  gain  negative  electrons  are  at  present  not 
sufficiently  well  defined  and  extensively  studied  to  indicate 
the  general  relations  existing  there. 

As  a  matter  of  convenience,  the  direction  in  which  the 
negative  electron  is  transferred  in  the  formation  of  a  chem- 
ical linking  may  be  indicated  by  an  arrow,  as  suggested 
by  J.  J.  Thomson,  the  head  of  the  arrow  giving  the  direction 
of  the  transfer  of  the  electron.  The  lines  representing 
linkings  as  written  heretofore  in  structural  formulas  will 
therefore  be  replaced  by  arrows;  H  — >  Cl  in  place  of  H  —  Cl, 
etc.  This  saves  the  cumbersome  use  of  plus  and  minus 
signs,  but  in  case  of  doubt  or  for  the  sake  of  clearness,  it  is 
also  advisable  to  use  these  signs  in  connection  with  the 
formulas. 


CHAPTER  II. 
VALENCE    (CONTINUED);    CO-ORDINATION  NUMBER. 

IT  has  been  emphasized  that  in  simple  compounds  the 
valence  is  the  capacity  of  an  atom  of  one  element  to  hold 
in  chemical  combination  a  certain  number  of  atoms  of 
some  other  element.  It  will  now  be  necessary  to  consider 
another  form  of  combining  capacity  which  appears  to  mani- 
fest itself  in  the  case  of  molecules  of  compounds  combining 
with  definite  numbers  of  molecules  of  some  other  com- 
pound. As  examples  may  be  mentioned  hydrates  such  as 
CaCl2.6H2O,  CrCl3.6H2O,  CuSO4.5H2O;  ammoniates  such 
as  AgC1.2NH3,  CuSO4.4NH3.H20;  and  double  salts  such 
as  4KCN.Fe(CN)2,  2KCl.PtCl4.  These  compounds  have 
as  components  simpler  compounds  which  are  combined  in 
definite  proportions  just  as  the  elements  in  the  simpler 
compounds  are  combined  in  definite  proportions.  It  be- 
comes evident,  therefore,  that  apparently  combining  capaci- 
ties of  molecules  for  other  molecules  exist  here  in  much  the 
same  way  as  in  the  case  of  the  combining  capacity  of  atoms 
for  other  atoms. 

A.  Werner,  in  the  last  twenty  years,  has  systematized 
compounds  of  varying  degrees  of  complexity.  In  order  to 
explain  the  formation  of  addition  compounds,  as  for  ex- 
ample, sulfur  trioxide  with  water,  ammonia,  hydrogen 
chloride,  etc.,  platinic  chloride  with  ammonia,  water, 
hydrogen  chloride,  etc.,  ammonia  with  water,  hydrogen 
chloride,  etc.,  he  makes  the  assumption  that  various  atoms 
such  as  the  sulfur  in  the  sulfur  trioxide,  the  platinum  in 
the  platinic  chloride,  and  the  nitrogen  in  the  ammonia,  etc., 
possess  a  residue  of  unsaturated  affinity,  which  permits 
such  groups  to  mutually  satisfy  each  other.  When  the 
amount  of  this  affinity  is  sufficient  to  bring  about  a  stable 

21 


22  CHEMICAL  REACTIONS. 

combination  between  the  single  molecules,  it  assumes  prac- 
tically the  same  role  as  the  ordinary  valence,  viz;  it  effects 
an  interdependence  between  two  elementary  atoms,  and  in 
this  way  unites  two  radicals  to  a  molecular  complex.  These 
new  valences  differ,  however,  from  ordinary  valences,  in 
that  they  are  not  able  to  unite  univalent  radicals  and  in 
order  to  distinguish  them  from  the  latter  he  calls  them 
"  auxiliary  valences . ' ' 

In  the  case  of  ammonium  chloride,  the  unsaturated 
auxiliary  valence  of  the  nitrogen  atom  in  the  ammonia 
would  be  saturated  by  the  auxiliary  valence  of  the  hydrogen 
atom  of  the  hydrogen  chloride.  The  formation  of  the 
ammonium  chloride  would  be  formulated  therefore  as 

H\  H\ 

H-)N  +  HCl  =  H-^N  •  •  •  HC1. 
H/  H/ 

"Since  according  to  this  formula,  four  hydrogen  atoms  are 
bound  to  nitrogen,  it  is  hardly  to  be  supposed  that  one 
hydrogen  atom  is  linked  up  by  a  greater  amount  of  affinity 
than  any  of  the  remaining  three;  it  is  far  more  probable 
that  a  state  of  equilibrium  is  reached  in  which  all  the 
hydrogen  atoms  are  linked  by  the  same  amount  of  affinity. 
Ammonium  is  therefore  a  complex  radical,  NH4,  in  which 
the  nitrogen  is  the  central  atom  having  the  four  hydrogen 
atoms  linked  to  itself  with  the  same  amount  of  affinity  in 
each  case.  On  each  hydrogen  atom  of  the  complex  NHk, 
there  is  still  a  certain  amount  of  unsaturated  affinity,  which 
the  radical  is  able  to  utilize  externally  to  itself  and  becomes 
in  this  way  monovalent.  Ammonium  salts  have,  therefore, 
the  following  structure: 


X. 

H 


E.  C.  C.  Baly  approached  this  general  question  in  a 
different  way.     His  views  may  be  stated  briefly  as  follows 


VALENCE;    CO-ORDINATION  NUMBER.  23 

(Jour.  Amer.  Chem.  Soc.  87,  979  (1915)) :  From  the  study 
of  the  absorption  in  the  ultraviolet  region  of  the  spectrum 
of  reacting  substances  before,  during,  and  after  the  reaction, 
he  concluded  that  every  chemical  molecule  is  surrounded 
by  a  condensed  force  field  of  electromagnetic  type.  If 
molecules  of  different  substances  are  brought  close  together, 
they  tend  to  form  an  associated  system,  or  addition  com- 
pound, with  a  loss  of  energy,  and  establishment  of  potential 
gradient.  If  this  potential  gradient  is  steep  enough,  a 
transfer  of  electrons  will  occur  with  the  formation  of  a 
true  chemical  compound.  Thus  the  compounds  HX  and 
YOH  may  unite  to  form  HX.YOH,  and  then  rearrange  to 
XY.H2O,  a  system  containing  less  energy  than  HX.YOH. 
If  the  force  lines  of  the  two  molecules  form  completely 
closed  systems,  no  reaction  will  occur  between  them  until 
their  force  fields  are  opened  up,  perhaps  by  molecules  of 
some  other  substance  as  the  solvent  or  a  catalyst. 

It  is  apparent  that  a  similarity  exists  between  the  views 
of  Werner  and  of  Baly  concerning  the  mechanism  involved 
in  the  formation  of  these  addition  compounds.     Both  con- 
sider that  simple  compounds  such  as  ammonia  and  hydrogen 
chloride  possess  unsaturated  properties,  Werner,  auxiliary 
valence,  and  Baly,  open  force  fields,  which  enable  these 
compounds    to    combine    to    form    addition    compounds. 
According  to  Werner,   after  the  two   simple  compounds 
come  together,  there  is  a  readjustment  of  this  affinity,  or 
auxiliary  valence,  between  the  nitrogen  atom  of  the  am- 
monia and  the  hydrogen  atom  of  the  hydrogen  chloride  in 
such  a  way  that  all  the  hydrogen  atoms  in  the  ammonium 
chloride  are  united  to  the  central  nitrogen  atom  in  the 
same  way,  while  the  chlorine  atom  is  held  finally  by  the 
new  res' dual  affinities  of  the  four  hydrogen  atoms  in  the 
NH4  radical.     Baly  considers  that  after  the  force  fields 
have  brought  the  two  simple  compounds  together  in  the 
case  of  a  compound  like  ammonium  chloride,  there  is  a 
3 


24  CHEMICAL  REACTIONS. 

readjustment  of  these  forces,  causing  a  formation  of  the 
stable  compound. 

If  the  valences  in  the  ammonium  chloride  are  assumed  to 
be  due  to  electrons  as  described  in  the  first  chapter,  then  the 

fe^it^a 

structure  of  the  compound  would  be    H  —  N          or>  mdi- 

x 


eating  the  direction  of  transfer  of  the  negative  electrons 

H-^     ^H 

by  means  of  arrows   H—  ^N^       "     This  formula  for  the 


structure  of  ammonium  chloride  has  all  the  advantages  of 
the  Werner  formula,  viz;  it  agrees  with  the  results  of  V. 
Meyer  and  M.  Lecco's  (Lieb.  Ann.  180,  173  (1876))  experi- 
ments that  the  four  hydrogens  bear  the  same  relation  to 
the  molecule,  and  it  shows  that  the  chlorine  bears  a  different 
relation  to  the  nitrogen  than  the  hydrogen.  Furthermore, 
it  has  the  advantage  over  Werner's  formula  in  that  only 
one  kind  of  valence  is  necessary.  Also,  it  is  readily  seen 
that  neither  oxidation  nor  reduction  is  involved  in  the 
formation  of  an  addition  compound  of  this  type.  If  only 
the  auxiliary  valence  idea  of  Werner  is  used  in  this  connec- 
tion, the  positions  of  the  electrons  are  not  definite,  so  that 
it  would  be  difficult  to  state  by  means  of  the  structures 
whether  any  oxidation  or  reduction  had  occurred. 

Many  compounds  similar  to  ammonium  chloride,  such 
as  derivatives  of  the  amines,  have  been  prepared  and 
studied.  These  compounds  were  for  some  time  thought 
to  follow  the  law  of  definite  proportions.  For  example, 
an  equal  number  of  molecules  of  amine  and  acid  combined 
to  form  the  definite  substituted  ammonium  salts.  Although 
this  generalization  appeared  to  hold  for  a  number  of  such 
compounds,  other  substances  were  prepared  after  a  time 
in  which  these  simple  relations  were  not  observed.  Thus, 
the  compound  (NH^HCl  (cf.  Werner,  Neuere  Anschauun- 


VALENCE;    CO-ORDINATION   NUMBER.  25 

gen)  was  prepared,  then  compounds  such  as  AgCl(NH3)2, 
PtCl4(NH3)2,  PtCl4(NH3)6,  CuS044NH3H20,  etc.,  which  did 
not  follow  such  simple  laws,  and  for  which  the  ordinary 
ideas  of  valence  did  not  suffice.  Some  of  these  compounds 
were  in  fact  termed  "anomalous,"  because  they  did  not  fall 
into  a  scheme  of  simple  formulas  as  it  was  expected  they 
should.  It  was  thought  that  the  reaction  between  am- 
monia or  an  amine,  and  hydrochloric  acid,  was  similar  to 
the  reaction  between  a  base  and  an  acid  to  form  a  salt, 
but  the  combinations  between  ammonia  and  salts  to  form 
the  compounds  just  indicated  showed  that  this  was  not 
the  case  and  that  ammoniates,  as  these  compounds  are 
called,  did  not  require  the  participation  of  an  acid. 

C.  Friedel,  in  1875  (Bull.  Soc.  Chim.  [2]  24,  160,  241), 
showed  that  in  cooling  a  solution  of  hydrogen  chloride  in 
ether,  a  crystalline  compound  was  formed  containing  an 
equal  number  of  molecules  of  ether  and  of  hydrogen 
chloride.  This  observation  was  an  isolated  one  for  some 
years.  J.  N.  Collie  and  T.  Tickle  (Trans.  Chem.  Soc.  75, 
710  (1899))  found  that  dimethyl  pyrone  formed  compounds 
with  the  halogen  hydrides  which  showed 
the  properties  characteristic  of  ammo-  H3C .  C  C .  CH3 
nium  halides,  and  later  were  found  to  JJQ  QJJ 

ionize  in  solution  in  a  manner  similar  ^9^ 

to  ammonium  salts,  and  were  therefore  O 

comparable  to  them.  A.  Baeyer  and 
V.  Villiger  (Ber.  34,  2679  (1901))  then  made  an  extended 
study  of  the  salts  formed  with  a  number  of  acids  by  different 
groups  of  oxygen  compounds  including  ethers,  ketones, 
esters,  etc.  These  salts  or  oxygen  compounds  are  analogous 
to  the  nitrogen  (ammonium)  compounds.  They  are  not 
as  stable  under  ordinary  conditions,  and  their  isolation  and 
preparation  in  quantity  for  study  is  difficult  for  most  of 
them.  Certain  acids  have  been  found  to  be  especially 
suitable  for  the  preparation  of  these  stable  oxonium  salts, 


26  CHEMICAL  REACTIONS. 

hydroferrocyanic  acid  (by  Baeyer  and  Villiger)  and  per- 
chloric acid  (by  K.  A.  Hofmann,  Ber.  43,  1080  (1910)). 
In  order  to  determine  whether  definite  compounds  are 
formed,  it  is  necessary  to  study  the  "  Property-Composition 
Curves"  of  mixtures  of  their  components,  such  as,  for 
example,  the  freezing-point  curves. 

The  application  of  the  principles  of  the  Phase  Rule  (cf. 
A.  Findlay's  "Phase  Rule,"  or  any  of  the  larger  modern 
text-books  of  general  chemistry)  shows  the  existence  of 
such  oxonium  salts  and  their  composition,  since  it  may  be 
stated  in  general  terms,  that  each  maximum  point  of  such 
a  freezing  point  curve  plotted  with  abscissas  as  relative 
content  of  the  two  components  in  the  mixture  and  ordinates 
as  the  freezing  points,  shows  such  a  compound  of  the  com- 
position given  by  the  point  on  the  abscissa  axis.  The 
application  of  such  studies  (and  of  analogous  studies  on  the 
properties  depending  upon  thermodynamic  relations  such 
as  vapor  pressure,  etc.)  to  aqueous  solutions  indicated  that 
compounds  of  water  and  salts  exist  similar  to  the  ammoni- 
ates.  It  is  readily  conceivable  that  the  hydrate  of  hydrogen 
chloride  may  be  compared  with  ammonium  chloride,  some 
of  the  chemical  properties  differing  because  of  the  difference 
between  nitrogen  and  oxygen.  This  question  will  be  taken 
up  again  later.  For  the  present,  reference  to  a  number  of 
papers  describing  such  compounds  may  be  given. 

Among  those  who  have  worked  in  this  field  may  be 
mentioned  J.  N.  Collie  and  T.  Tickle,  Trans.  Chem.  Soc. 
75,  710  (1899);  J.  N.  Collie;  Ibid.  85,  971  (1904);  A.  Baeyer 
and  V.  Villiger,  Ber.  34,  2679,  3612  (1901);  35,  1201  (1902); 
S.  Hoogewerff  and  W.  A.  van  Dorp,  Rec.  trav.  china.  21, 
349  (1902);  J.  Thiele  and  F.  Strauss,  Ber.  36,  2375  (1903); 
D.  Vorlander,  Lieb.  Ann.  841,  1  (1905);  V.  A.  Plotnikoff, 
J.  Russ.  phys.  chem.  Ges.  36,  1088  (1904);  40,  64  (1908); 
H.  Stobbe,  Lieb.  Ann.  370,  93  (1909);  K.  A.  Hofmann  and 
co-workers,  Ber.  43,  178,  183,  2624  (1910);  D.  Mclntosh, 


VALENCE;    CO-ORDINATION  NUMBER.  27 

Jour.  Amer.  Chem.  Soc.  32,  542  (1910);  0.  Maass  and  D. 
Mclntosh,  Ibid.  34,  1273  (1912);  35,  535  (1913);  M. 
Gomberg  and  L.  H.  Cone,  Lieb.  Ann.  376,  183  (1910);  J. 
KendaU,  Jour.  Amer.  Chem.  Soc.  86,  1222,  1722  (1914); 
J.  Kendall  and  C.  D.  Carpenter,  Ibid.  86,  2498  (1914); 
J.  Kendall  and  W.  A.  Gibbons,  Ibid.  37,  149  (1915);  as  well 
as  a  number  of  others. 

Water,  then,  may  add  to  salts  to  form  the  so-called 
"water  of  crystallization"  or  hydrates  in  a  way  similar  to 
the  action  of  ammonia. 

The  structures  of  some  of  the  simpler  molecular  com- 
pounds will  now  be  developed  before  going  on  to  the  more 
complex  ones  and  the  double  salts.  Ammonia  is  formulated 

r=  +  +    — 

NH3,  hydrogen  chloride,  HC1,  and  ammonium  chloride, 

-+  +   — 

NH4C1.     The  state  of  oxidation  of  nitrogen  in  ammonia 

and  in  ammonium  chloride  is  the  same,  —  3  and  —  4+1 
=  —  3.  The  difference  in  the  nitrogens  consists  in  the 
fact  that  one  negative  electron  was  taken  up  and  one  given 
off  in  the  formation  of  the  ammonium  salt.  A  comparison 
of  the  similar  simple  molecular  compounds  of  other  elements 
brings  to  light  the  same  fact,  that  in  each  the  "central" 
element  takes  up  and  gives  off  a  negative  electron  in  forming 
the  molecular  compound  but  does  not  change  its  state  of 
oxidation.  Thus,  there  may  be  mentioned  phosphonium 
(state  of  oxidation  of  phosphorus  —  4  +  1  =  —  3),  sul- 
fonium  (-  3  +  1  =  -  2),  oxonium  (-  3  +  1  =  -  2), 
iodonium  (—  2  +  1  =  —  1),  selenonium  (—  3  +  1  =  —  2), 
arsonium  (—  5  +  1  =  —  4),  stannonium  (—  3  +  1  =  —  2), 
and  stibonium  (—  5  +  1  =  —  4)  compounds. 

The  characteristic  property  of  these  simple  molecular 
compounds,  which  may  be  grouped  under  the  name  of 
"onium  compounds,"  is  the  fact  that  the  atoms  or  groups 
combined  directly  with  the  "onium"  forming  or  central 
element,  act  as  a  unit  with  the  central  atom  in  many  phys- 
ical and  chemical  transformations  and  are  often  termed 


28  CHEMICAL  REACTIONS. 

radicals.  This  is  shown  for  physical  phenomena  in  the  con- 
duction of  the  electric  current  where  these  groups  act  very 
often  as  ions,  arid  in  chemical  reactions  in  metatheses  where 
the  groups  are  capable  of  replacing  other  atoms  or  groups. 

When  ammonia  is  added  to  platinic  chloride,  it  appears 
that  two  methods  of  combination  exist.  The  first  two  mole- 
cules of  ammonia  add  to  form  the  compound  PtCl4.2NH3, 
which  is  not  ionized  in  solution,  and  does  not  yield  a  precipi- 
tate of  silver  chloride  when  treated  with  silver  nitrate.  If 
a  compound  containing  a  third  molecule  of  ammonia  is 
prepared,  *PtCl4.3NH3,  this  substance  ionizes  and  one  of 
the  four  chlorine  atoms  may  be  precipitated  by  silver 
nitrate.  The  third  ammonia  molecule  evidently  exerts  a 
different  influence  in  the  molecule  than  the  other  two.  In 
the  substance  PtCl4.4NH3,  two  chlorine  atoms  are  ionized, 
while  in  PtCl4.6NH3,  four  chlorines  are  ionized.  The  last 
four  ammonia  molecules  play  a  different  part  from  the 
first  two  in  causing  the  chlorine  to  assume  new  properties. 
The  hydrates  of  chromic  chloride  show  similar  phenomena. 
The  electrical  conductivity  of  the  greyish  blue  hydrate, 
CrCl3.6H2O,  is  practically  constant,  four  ions  are  present, 
and  all  the  chlorine  may  be  precipitated  with  silver  nitrate. 
In  a  freshly  prepared  solution  of  the  isomeric  green  com- 
pound at  0°,  only  one  third  of  the  chlorine  is  precipitated 
by  silver  nitrate,  and  the  conductivity  at  first  is  much  less 
than  that  of  the  former,  but  increases  gradually,  until  it 
finally  reaches  the  same  value  as  that  of  the  other  isomer. 
The  chlorine  in  these  two  compounds  is  evidently  combined 
differently.  Three  hydrates  of  chromic  chloride,  having 
the  composition  CrCls.GH^O,  are  known.  In  one,  one 
chlorine  may  ionize,  in  another  two  chlorines  ionize,  and  in 
the  third  all  the  chlorines  are  ionic  in  solution  (cf.  Werner, 
Neuere  Anschauungen,  III  Edition,  (1913)  p.  333). 

It  has  been  stated  that  platinic  chloride  will  add  ammonia 
just  as  hydrogen  chloride  does.  The  only  difference  at  the 


VALENCE;    CO-ORDINATION  NUMBER.  20 

present  time  is  that  the  ammonia  can  exert  two  distinct 
influences  or  can  add  in  two  ways  in  connection  with 
platinum  chloride,  while  it  is  probable  that  it  can  add  in 
one  way  only  to  hydrogen  chloride,  although  an  allotropic 
modification  of  ammonium  chloride  was  described  recently 
(F.  E.  C.  Scheffer,  Chemical  Abstracts  10,  411  (1916)). 

Ammonium  chloride  in  aqueous  solution  yields  chlorine 
ions  just  as  the  platinum  chloride-ammonia  compound, 
2NH3.PtCl4  with  1,  2,  3,  or  4  additional  molecules  of 
ammonia  does.  Since  ionization  was  pointed  out  as  a 
characteristic  property  determining  in  which  way  the  am- 
monia had  added  to  the  platinic  chloride  or  the  influence 
it  exerted  in  the  compound,  it  is  likely  that  the  ammonia 
in  the  ammonium  chloride  is  combined  with  the  hydrogen 
chloride  in  the  same  way  that  the  ammonia  is  combined 
with  the  platinic  chloride  when  the  chlorines  of  the  latter 
become  ionic.  If,  therefore,  the  structure  of  ammonium 
chloride  is  known,  it  is  possible  to  assign  a  structure  to  the 
addition  compounds  of  platinic  chloride  and  ammonia  as 
far  as  the  ammonia  molecules  which  cause  the  chlorine 
atoms  to  become  ionic  are  concerned. 

Since  diammono  platinic  chloride,  (NH3)2PtCl4,  combines 
with  ammonia  in  a  similar  way  to  that  of  hydrogen  chloride, 
the  structure  of  the  addition  product  may  be  written  in  a 
(NH3)2  Pt  C13 

TT          \ 

similar  way,  namely  "^  N  —  ^Cl    Introducing  succes- 


sive  molecules  of  ammonia,  analogous  structures  follow, 
until  when  all  four  chlorines  are  ionizable,  the  structure 

HHH    HHH 

\\S       \IS 
CK-N  N—  Cl 


Cl—  N  N-C1 

/t\      /\\ 
HHH   HHH 


30  CHEMICAL  REACTIONS. 

or  (NH3)2Pt(->NH3  -»  Cl)4  is  obtained.  The  question 
which  now  presents  itself  is  the  way  in  which  the  other  two 
molecules  of  ammonia  are  combined  in  the  last  compound 
and  also  in  (NHs^PtCU.  The  only  evidence  which  is 
available  is  that  starting  with  platinic  chloride,  in  which 
the  valence  of  the  platinum  is  +  4,  no  oxidation  or  reduction 
of  any  of  the  atoms  is  observable  when  the  successive 
molecules  of  ammonia  are  added.  Platinic  chloride  is  also 
capable  of  adding  two  molecules  of  hydrogen  chloride, 
forming  H2PtCl6,  in  which  two  hydrogen  atoms  are  ioniz- 
able.  This  last  reaction  indicates  that  platinum,  like 
nitrogen,  is  capable  of  acting  as  an  onium  element,  forming 
molecular  compounds.  If  this  assumption  is  made,  then 
the  structures  of  the  combinations  can  be  expressed  as 


etc.  In  this  way,  only  one  kind  of  valence  is  present,  and, 
so  long  as  no  evidence  exists  against  these  structures,  and 
evidence  (partly  indirect,  it  is  true)  in  favor  of  them,  they 
will  be  adopted. 

In  writing  the  structures  of  addition  compounds,  Werner 
indicates  auxiliary  valence  by  dotted  lines  and  ordinary 
valence  by  full  lines.  This  is  illustrated  by  his  structure 

H3N^  Cl 

for  the  di-ammoniate  of  platinic  chloride,  H3N—  -  Pt  —  Cl 

C\^  ^C\ 

When  additional  molecules  of  ammonia  combine  with  the 
di-ammoniate,  Werner  considers  these  ammonia  molecules 
to  be  held  by  auxiliary  valences  in  the  same  way  as  the 
first  two  ammonia  molecules,  or  in  other  words,  that 
ammonia  adds  to  the  platinum  in  one  way  only.  This  is 
different  from  the  idea  developed  here.  Since  the  addition 


VALENCE;    CO-ORDINATION  NUMBER. 


31 


of  the  third,  etc.,  molecules  of  ammonia  give  rise  to  ionic 
chlorine,  Werner  considers  that  the  entering  ammonia 
takes  a  position  between  the  platinum  atom  and  the 
chlorine  atom,  crowding  the  latter  away  from  the  central 
platinum  atom  into  a  separate  zone.  Since  the  distance  of 
the  chlorine  atom  from  the  central  platinum  is  greater  than 
when  it  is  bound  directly,  the  latter  acquires  different 
chemical  properties,  which  manifest  themselves  in  the  ionic 
character  of  the  chlorine,  etc.  (Werner).  Thus,  the  indirect 
union  is  characterized  by  ionic  properties.  Atoms  which 
are  directly  attached  to  another  atom  either  by  principal  or 
auxiliary  valence  are  in  the  first  zone.  The  number  of 
atoms  or  of  molecules  in  the  first  or  inner  zone  determines 
the  "Co-ordination  Number."  Atoms  which  are  indirectly 
joined  to  the  central  atom  are  in  the  second  or  outer  zone. 
Werner  writes  the  structures  for  the  ammoniates  of 
platinic  chloride  containing  more  ammonia  than  di-am- 
moniate,  as  follows: 


H3N. 


H3N— ;pt—  ci 

H3N'"        ^Cl 


Cl; 


H3N— -Pt  — Cl 


CL 


H3N 
H8N- 


:Pt---NH 


Cl3,etc. 


The  question  of  nomenclature  is  an  important  one  and 
must  be  considered  in  this  connection.  Werner  introduced 
certain  terms  in  the  development  of  his  theory  involving 
main  and  auxiliary  (or  secondary)  valences,  and  these 
terms  are  useful.  The  consideration  of  a  group  in  a  mole- 
cule in  which  the  atoms  react  as  a  unit,  as  the  inner  zone 
or  sphere,  and  another  group  as  the  outer  zone  is  used  by 
Werner,  the  former  to  denote  the  group  consisting  of  the 
central  atom  combined  with  other  atoms  or  groups  by 


32  CHEMICAL  REACTIONS. 

auxiliary  or  principal  valences  and  ionizing  in  solution. 
The  method  introduced  by  Werner  of  writing  these  groups 
is  extremely  convenient,  the  inner  zone  being  enclosed 
in  brackets.  The  expressions  inner  zone  and  outer  zone 
and  the  use  of  brackets  will  be  followed  in  this  book,  but 
the  significance  of  the  combinations  between  the  atoms 
from  the  point  of  view  of  the  electron  conception  of  valence 
must  be  kept  strictly  in  mind.  In  using  the  terms  intro- 
duced by  Werner,  it  is  not  intended  to  endow  the  groups 
with  the  physical  significance  which  the  meanings  of  the 
words  might  imply.  The  expressions  inner  zone  and  outer 
zone  simply  mean  different  groups  which  have  a  partially 
independent  existence  under  special  conditions  (the  most 
common  one  being  in  solution),  and  the  atoms  comprising 
such  a  group  act  as  a  unit  very  often.  The  terms  inner  and 
outer  mean  nothing  more  and  must  be  looked  upon  as  a 
convenient  phraseology. 

The  force  field  theory  of  Baly  assumes  the  primary  forma- 
tion of  an  addition  product,  which,  under  certain  conditions 
can  become  a  definite  compound  in  which  the  atoms  are 
combined  by  ordinary  valences.  The  views  outlined  here 
may  be  used  similarly.  The  first  addition  of  ammonia  and 
hydrogen  chloride  may  produce  a  compound  H3N  ^±  HC1, 
or  H3N  ;±  C1H,  presumably  the  former  by  analogy  as  will 
be  pointed  out  later,  and  this  then  rearranges  or  tauto- 
merizes  to  the  more  usual  form  H4NC1.  These  two  steps 
correspond  to  the  steps  of  Baly.  The  onium  valence  corre- 
sponds jn  a  number  of  compounds  to  the  auxiliary  valence 
of  Werner,  and  the  reaction  just  given  may  be  stated  in 
Werner's  terms  as  due  to  a  compound  being  formed  of 
molecules  combined  by  an  auxiliary  valence,  which  under 
certain  conditions  may  become  principal  valences.  The 
views  given  here  have  an  advantage  over  other  views  in 
postulating  only  one  kind  of  valence,  and  in  keeping  the 
difference  between  valence  and  chemical  affinity  strictly 
in  mind. 


VALENCE;    CO-ORDINATION  NUMBER. 


33 


The  structures  developed  with  platinic  chloride  can 
evidently  be  applied  to  a  great  number  of  compounds,  such 
as  hydrates,  other  ammoniates,  and  molecular  compounds 
in  general.  A  comparison  of  the  structures  of  hexammono- 
platinic  chloride  and  the  hexahydrate  of  calcium  chloride 
will  show  this: 


Cl- 


+    +1 

HSN 


-4 

NH^ 

^-4 
+-1  + 


_4  //      \      -4      ' 

+    +1X/  \+l  + 

H,NX  NH,--C1 


-Cl 

ci 


-3 

+  +1 


+1 


+  6    /-3 

-H 


-3  // 

+  +1J/ 

Hr\r 
oU 


Cl 


From  the  foregoing  it  is  evident  that  the  co-ordination 
number  of  the  platinum  in  platinic  chloride  di-ammoniate, 
(NH3)2PtCl4,  or  in  platinic  chloride  hexa-ammoniate, 
(NH3)2PtCl44NH3,  is  six,  while  the  co-ordination  number 
of  nitrogen  in  ammonium  chloride  is  four,  etc. 

Calcium  chloride  may  combine  with  six,  four,  or  two, 
molecules  of  water  of  hydration  or  exist  in  the  anhydrous 
state.  The  co-ordination  number  of  the  calcium  in  the 
hexahydrate  is  six,  but  what  it  is  in  the  tetrahydrate  is 
difficult  to  say,  since  it  is  not  known  whether  the  chlorine 
is  in  the  inner  or  outer  zone.  In  the  di-hydrate  it  may 
be  four,  and  in  the  zero  hydrate  it  can  only  be  two. 
The  external  physical  conditions  such  as  concentration, 
vapor  pressure,  and  temperature,  determine  the  number  of 
molecules  of  water  of  hydration  of  the  calcium  chloride. 
This  shows  that  the  co-ordination  number  of  the  calcium 
is  dependent  upon  external  conditions  just  as  the  ordinary 
valence  is. 

Calcium  chloride  combines  with  eight  molecules  of  am- 
monia, or  the  calcium  has  the  co-ordination  number  eight 
in  this  compound.  A  large  number  of  salts  have  been 
found  to  crystallize  with  six  molecules  of  water.  With 
regard  to  ammonia,  copper  sulfate  can  combine  with  four 


34  CHEMICAL  REACTIONS. 

molecules,  silver  chloride  with  two,  etc.  Werner  showed 
that  the  co-ordination  number  of  an  element  is,  in  general, 
four,  six,  or  eight. 

These  definite  numbers  show  a  capacity  for  combination 
and  are  therefore  of  the  nature  of  valence  numbers.  They 
are  not  identical  with  the  atomic  valence  as  already  defined, 
which  is  due  to  the  transfer  of  a  negative  electron,  but 
indicate  a  different  kind  of  capacity  factor  of  chemical 
energy.  The  manner  in  which  this  is  to  be  interpreted,  and 
the  underlying  properties  upon  which  it  depends,  cannot 
be  settled  at  present.  A  possible  suggestion  that  it  depends 
upon  spacial  configuration  and  arrangement  of  the  atoms 
around  a  central  atom  may  be  put  forward.  The  stereo- 
chemistry of  the  compounds,  as  shown  by  A.  Werner,  the 
deductions  of  T.  V.  Barker,  and  the  theoretical  and  experi- 
mental researches  of  W.  H.  and  W.  L.  Bragg  and  of  A.C. 
Crehore,  point  in  this  direction.  Whatever  the  cause  may 
be,  this  capacity  factor  exists,  and  as  shown,  may  be  inter- 
preted by  means  of  the  general  valence  linkings  of  the 
electron  conception.  In  the  later  chapters,  the  significance 
of  co-ordination  number  in  this  sense  is  used  where  reference 
is  made  to  a  definite  combining  capacity  of  this  nature. 

Although  the  platinum  atom  in  the  ammoniates  of 
platinic  chloride  has  been  considered  as  the  central  atom, 
the  nitrogen  of  the  ammonia  (except  with  the  first  two 
molecules  of  ammonia)  also  may  be  taken  to  be  the  central 
atom.  Thus,  when  the  di-ammoniate,  (NH3)2PtCl4,  com- 
bines with  ammonia,  it  really  plays  the  same  part  as  the 
hydrogen  chloride  in  the  formation  of  ammonium  chloride. 
In  both  cases,  the  chlorine  of  the  hydrogen  chloride  and 
of  the  di-ammoniate,  (NH3)2PtCl4,  becomes  ionic.  The 
structures  for  the  tri-ammoniate,  (NH3)2PtCl4NH3,  and 
ammonium  chloride  are  analogous: 


_ 

H  H 


Cl 


VALENCE;    CO-ORDINATION   NUMBER.  35 

When  hydrogen  chloride  and  platinic  chloride  combine 
to  form  the  addition  compound,  chlorplatinic  acid,  H^PtCle, 
the  platinic  chloride  plays  a  role  somewhat  similar  to  that 
of  ammonia  in  the  formation  of  ammonium  chloride,  that 
is,  both  are  added  to  hydrogen  chloride.  There  is  a  differ- 
ence, however,  in  that  the  addition  of  platinic  chloride  to 
hydrogen  chloride  causes  the  hydrogen  of  the  hydrogen 
chloride  to  become  ionic,  while  the  addition  of  ammonia  to 
hydrogen  chloride  causes  the  chlorine  of  the  hydrogen 
chloride  to  become  ionic.  In  other  words,  in  the  first  case, 
the  hydrogen  is  in  the  outer  zone;  in  the  second,  the 
chlorine  is  in  the  outer  zone.  Since  ionogens  are  produced 
in  both  cases,  both  the  ammonia  and  the  platinic  chloride, 
according  to  Werner,  enter  between  the  hydrogen  and  the 
chlorine  atoms  in  the  hydrogen  chloride.  In  one  case,  the 
hydrogen  is  crowded  out  into  the  outer  zone,  while  in  the 
other,  it  is  the  chlorine  of  the  hydrogen  chloride.  Accord- 
ingly, the  structures  of  the  two  compounds  may  be  written 


and 


The  two  complexes,  (PtCle)  and  (NKt),  bear  the  same 
relation  in  the  addition  compounds,  the  only  difference 
being  that  the  charges  have  different  signs,  the  former 
being  negative  and  the  latter  positive.  The  reason  for  this 
lies  in  the  electrical  nature  of  the  two  central  atoms. 
Platinum  is  an  electro-positive  element,  and  nitrogen  in 
ammonia  is  an  electro-negative  element.  It  becomes  evi- 
dent in  looking  over  a  large  number  of  complex  salts,  that 
they  ionize  in  such  a  way  that  the  element  in  the  outer 
zone  has  an  electric  charge  of  the  same  sign  as  that  of  the 
central  atom  to  which  it  is  attached.  Thus,  in  addition, 
of  those  with  positive  central  atoms,  potassium  ferro-  and 
ferri-cyanides,  where  the  positive  iron  atom  serves  as  the 


36  CHEMICAL  REACTIONS. 

central  atom,  potassium  chromium  oxalate, 
may  be  quoted  out  of  the  great  number  with  which  the 
reader,  no  doubt,  is  familiar.  As  compounds  of  the  type 
in  which  the  central  atom  is  negative,  may  be  mentioned 
besides  ammonium  chloride,  and  the  tri-ammoniate,  tetra- 
ammoniate,  etc.,  of  platinic  chloride,  the  hydrates  of  calcium 
chloride,  aluminium  chloride,  chromium  chloride,  etc.,  since 
in  these  hydrates  just  as  in  the  ammoniates,  the  oxygen  of 
the  water  may  serve  as  the  central  atom. 

It  has  been  stated  that  water  like  ammonia  can  be  added 
in  two  ways  in  the  formation  of  addition  compounds  such 
as  the  hydrates,  calcium  chloride  hexahydrate,  etc.,  similar 
to  the  ammonia  in  the  hexa-ammoniate  of  platinic  chloride, 
PtCLiGNHa.  When  platinic  chloride  is  dissolved  in  water, 
the  aqueous  solution  does  not  contain  chloride  ion  as  would 
be  expected  if  the  water  combined  with  the  chloride  as  the 
ammonia  does.  The  platinic  chloride  combines  with  the 
water,  however,  to  form  the  di-hydrate,  PtC^H^O,  which 

-I- 

is  an  acid  and  yields  the  ions  2H  and  PtCl4(OH)2,  and  should 
therefore  be  formulated  H2PtCl4(OH)2.  The  water  behaves 
towards  the  platinic  chloride  just  as  the  hydrogen  chloride 
does  in  the  formation  of  the  chlorplatinic  acid,  H^PtCls. 
The  platinic  chloride  enters  between  the  hydrogen  and  the 
hydroxyl  of  the  water  molecule,  analogous  to  the  way  it 
does  in  the  case  of  hydrogen  chloride,  and  in  each  case 
forces  or  transfers  the  hydrogen  into  the  outer  zone.  The 
structures  of  the  two  complexes,  PtCl4(OH)2  and  PtCl6^ 
ought  therefore  to  be  alike.  They  may  be  written  as 
follows : 

Cl  Cf 


a         and         Lcf          ,a 

I  II 

The  water  molecule  here  has  added  as  H  and  OH.     In  order 


VALENCE;    CO-ORDINATION  NUMBER. 


37 


to  get-  a  definite  picture  of  the  differences  between  the  three 
ways  in  which  water  can  function  in  these  addition  com- 
pounds, the  reader  may  compare  structure  I  with  the  struc- 
ture of  the  hexa-hydrate  of  calcium  chloride.  With  the 
latter,  part  of  the  water  enters  between  the  calcium  and 
chlorine  atoms,  producing  chloride  ions,  and  part  of  the 
water  is  simply  added  to  the  calcium  atom  by  onium  valence 
or  " auxiliary"  valence  or  "force  field,"  symbolized  by 
the  two  arrows  in  opposite  directions.  It  was  stated 
previously  that  the  first  stage  in  the  formation  of  ammonium 
chloride  from  ammonia  and  hydrogen  chloride  may  be  the 
formation  of  a  primary  addition  compound,  H3N  *=*  HC1, 
due  simply  to  the  onium  valence,  or  the  auxiliary  valence 
or  the  force  field  between  the  nitrogen  and  the  hydrogen 
atoms,  and  that  this  preliminary  compound  then  tauto- 
merizes  into  (NH4)C1  with  the  chlorine  in  the  outer  zone. 
Now  this  preliminary  stage  possibly  may  occur  in  the  for- 
mation of  all  these  addition  compounds,  no  matter  what  the 
subsequent  rearrangement  happens  to  be.  Thus,  in  the  for- 
mation of  the  hexa-hydrate  of  calcium  chloride,  all  the  mole- 
cules of  water  first  may  add  to  the  calcium  atom  through  the 
force  field,  and  then  tautomerism  may  set  in,  the  chlorine 
leaving  the  calcium  to  combine  with  the  oxygen  of  the  water. 


Ca 


-Cl 
^Cl 


H2 
X3- 
-O- 
H2 


Cl 
Cl 


Similarly  with  the  di-hydrate  of  platinic  chloride, 
H2PtCl4(OH)2,  all  the  water  molecules  may  add  to  the 
platinum  atom  through  the  force  field  first  and  then  rear- 
rangement set  in  and  the  hydrogens  become  ionic. 


Cl, 

cr 
ci' 


:Pt 


OH, 


OH, 


-H 

H 


38  CHEMICAL  REACTIONS. 

In  the  case  of  the  hexa-ammoniate  of  platinic  chloride, 
the  ammonia  may  behave  in  a  way  analogous  to  that  of 
the  water  in  the  hexahydrate  of  calcium  chloride.  Whether 
or  not  all  the  water  molecules  or  ammonia  molecules  must 
first  be  combined  with  the  platinum  or  calcium  atoms  in 
this  way  before  any  tautomerism  can  take  place,  it  is  im- 
possible to  say. 

Potassium  chloride  adds  to  platinic  chloride,  in  the  same 
way  that  hydrogen  chloride  does,  forming  potassium  chlor- 
platinate.  The  latter  would  therefore  have  a  structure 


similar  to  that  of  the  acid,  or : 


C1x  S^K 

ci—  Pt^c 


Just  as  in 


_CK        ^( 

the  case  of  the  formation  of  the  other  addition  compounds, 
here,  too,  probably,  the  intermediate  stage  may  occur 
where  the  potassium  chloride  is  added  to  the  platinum 
atom  in  the  onium  way  and  then  rearranges,  the  potassium 
going  into  the  outer  zone. 

It  is  well  known  that  ammonium  chloride  can  add  to 
platinic  chloride  just  as  potassium  chloride  does,  forming 
the  ammonium  chlorplatinate.  Chlorplatinic  acid,  H^PtCJe, 
adds  to  ammonia  just  as  hydrogen  chloride  does,  forming 
the  ammonium  chlorplatinate;  the  di-ammoniate  of  platinic 
chloride  adds  to  hydrogen  chloride,  forming  ammonium 
chlorplatinate.  In  each  of  the  above  cases  an  addition 
compound  plays  the  same  role  as  a  simple  compound, 
forming  addition  compounds  with  other  molecules. 

From  what  has  been  said  in  regard  to  the  probable 
structures  of  the  hexachlorplatinic  acid,  H2PtCl6,  and  the 
tetrachlorplatinic  acid,  H2PtCl4(OH)2,  it  is  possible  to  assign 
structures  to  the  whole  series  of  platinic  acids,  as  Werner 
has  done  (Neuere  Anschauungen  auf  dem  Gebeite  der 
anorganischen  Chemie,  3d  ed.  (1913),  pp.  40-1). 


VALENCE;    CO-ORDINATION  NUMBER. 


39 


Cl — Pt— Cl 


Cl—  Pt—  Cl 


X 


O—  H 


-Cl 


',  \0-H 


Chlorplatinic 
acid 

=       +~ 
6    xO — H 

ci— Pt— 5— H 

\/     ^0— fi 

Trichlorplatinic  acid 
(not  known) 


Pentachlorplatinic 
acid 


Tetrachlorplatinic 
acid 


H 


Cl\     + 6 

-I-       •=     >»—*/  =       -f- 
H— 0 Pt— 0— H 

H— 6^ 


^0— H 

Monochlorplatinic 
acid 


CK    ±|   /O — H 

Cl— Pt— O— H 

H — 0-^^     ^^0 — H 

Dichlorplatinic 
acid 

-+  =.  =  4— 

H — Os.    4-6  /O — H 
H — O— Pt— 0— H 

Platinic 
"acid 


The^fact  that  these  acids  are  all  dibasic  proves  that  the 
acidity  is  not  connected  with  the  hydrogen  of  the  hydroxyl 
groups,  and  by  comparing  the  whole  series  from  chlor- 
platinic  acid  to  platinic  acid,  it  is  evident  that  the  ionizable 
hydrogens  are  those  combined  directly  with  the  positive 
central  atom,  platinum  in  this  case.  The  salts  of  these 
acids  have  similar  structures. 

It  will  have  been  observed  that  tautomerism  has  been 
spoken  of  a  number  of  times  as  occurring  with  different 
compounds.  The  idea  of  tautomerism  is  familiar  from 
organic  chemistry,  but  it  appears  to  be  of  much  wider 
applicability  than  has  been  heretofore  assumed  (cf.  also 
W.  C.  Bray  and  G.  E.  K.  Branch  as  well  as  G.  N.  Lewis, 
Jour.  Amer.  Chem.  Soc.  1440-1455  (1914)).  In  tautomeric 
rearrangements,  none  of  the  atoms  in  the  molecules  is 
reduced  or  oxidized;  each  remains  in  the  same  state  of 
oxidation  as  before.  This  is  brought  out  by  the  following 
formulas  which  represent  the  tautomeric  forms  of  a  number 
of  substances: 

1C 


and 
and. 


H-»N: 
H4N-»C1 


40  CHEMICAL  REACTIONS. 

and 


and     (H3N)2^Pt(Cl3)  ->NH3  ->C1 

(H26)2^:PtCl4   and    H2PtCl4(OH)2, 
and  so  on. 

These  examples  show  the  possibilities  of  tautomerism  in 
inorganic  compounds.  The  valence  or  state  of  oxidation 
of  none  of  the  atoms  has  changed.  Although  tautomeric 
changes  in  molecules  will  be  used  in  the  later  chapters,  it 
will  not  be  referred  to  explicitly  or  in  detail. 


CHAPTER  III. 

ACIDS  AND  BASES. 

THE  valence  views  upon  which  the  structures  and  classi- 
fication of  substances  depend  have  been  given  in  some 
detail  in  the  preceding  chapters.  Before  proceeding  to 
consider  the  theory  of  chemical  reactions  which  it  is  desired 
to  emphasize  here,  some  further  applications  of  the  valence 
views  may  be  of  interest.  Acids  and  bases  form  two  of  the 
most  interesting  and  widely  studied  groups  of  substances 
in  chemistry,  and  the  bearing  of  the  theoretical  relations 
described  upon  their  reactions  and  formulations  will  be 
given.  The  considerations  bear  also  upon  the  state  of 
substances  in  solution. 

The  theoretical  view  of  the  chemical  nature  of  acids  was 
put  upon  a  very  much  more  satisfactory  scientific  basis  by 
Arrhenius  in  1887.  He  showed  that  the  acid  properties  of 
substances  in  solution  depended  upon  the  presence  of  hydro- 
gen ion,  and  that  the  concentration  of  this  hydrogen  ion 
could  be  measured  in  a  number  of  different  ways.  In  the 
electrolytic  dissociation  in  solution  in  which  the  positive 
hydrogen  ion  is  produced,  the  rest  of  the  molecule  forms 
the  negative  ion,  but  for  the  characteristic  properties  of 
the  acid  only  the  hydrogen  is  of  importance. 

The  theory  of  ionization  in  solution  showed  that  hydrogen 
ions  are  the  essential  constituents  of  acids.  However,  the 
part  played  by  the  solvent  in  the  ionization,  or  in  other 
words,  the  probable  mechanism  of  reaction  according  to 
which  the  ions  are  produced,  is  not  shown  in  the  theory  of 
Arrhenius.  It  is  true  that  the  relative  degrees  of  ionization 
of  substances  in  different  solvents  were  shown  to  be  paral- 
leled by  certain  other  properties  of  the  solvent,  such  as  the 
dielectric  constant,  and  that  combination  of  the  solvent 

41 


42  CHEMICAL  REACTIONS. 

with  the  ion  has  been  proven  to  exist  in  a  number  of  cases, 
but  these  facts  are  far  from  a  satisfactory  theory  of  the 
reactions  taking  place  when  a  substance  is  considered  to 
undergo  ionization. 

The  views  of  Werner  with  regard  to  acids  may  be  stated 
in  the  form  in  which  he  summarized  them  (Neuere  An- 
schauungen,  pp.  273-275),  (1)  There  are  anhydro  acids 
and  aquo  acids.  (2)  Every  compound  which  can  form  a 
hydrate  with  water,  and  which  then  yields  hydrogen  ions 
in  aqueous  solution  as  a  product  of  ionization,  is  an  anhydro 
acid.  (3)  Every  hydrate  which  ionizes  in  aqueous  solution 
yielding  hydrogen  ions,  is  an  aquo  acid,  or  in  short,  an  acid- 
In  terms  of  the  ionic  electrochemical  viewpoint,  the  follow- 
ing definition  is  given  by  Werner  for  an  anhydro  acid: 
A  compound  which,  in  aqueous  solution,  combines  with  the 
hydroxyl  ions  of  the  water,  and  in  this  way  shifts  the 
equilibrium  for  the  electrolytic  dissociation  of  water  to  a 
limiting  value  for  the  hydrogen  ion  concentration  character- 
istic for  the  compound,  is  an  anhydro  acid. 

These  views  of  Werner,  involve  a  theory  of  the  mechanism 
of  acid  production  in  solution,  and  are  of  general  interest. 
The  structures  which  he  gives  are  of  the  same  nature  as 
those  he  gives  for  salts,  etc.,  as  will  be  seen  presently  when 
comparing  them  with  the  structures  developed  in  connection 
with  the  electron  conception  of  valence. 

The  views  with  regard  to  acids  which  follow  from  the 
electron  conception  of  valence  and  from  the  principles 
outlined  in  the  earlier  chapters  will  now  be  given. 

It  will  be  of  interest  to  take  up  a  number  of  acids  contain- 
ing oxygen.  Sulfuric  acid  may  serve  as  a  typical  example. 
Its  structure  is  formulated  ordinarily  as: 

OH 


This  structure  is  based  upon  a  number  of  experimental 


ACIDS  AND  BASES.  43 

facts,  such  as  the  reactions  of  organic  derivatives  of  the 
acid  and  related  compounds,  the  successive  replacement  of 
the  hydroxyl  groups,  etc.  From  the  discussion  of  the 
platinum  acids  in  the  preceding  chapter,  it  appears  to  be 
highly  improbable  ~or  a  substance  possessing  this  structure 
to  ionize  as  an  acid.  If,  however,  the  structure  is  written 
in  the  tautomeric  form,  this  difficulty  disappears  and  sul- 
furic  acid  falls  in  line  with  the  platinum  acids.  The  tauto- 
meric forms  of  sulfuric  acid  are: 


The  formation  of  dibasic  acids  through  the  addition  of  water 
to  both  sulfur  trioxide  and  platinic  chloride  becomes,  from 
the  above  considerations,  a  similar  phenomenon.  Accord- 
ing to  the  older  view,  the  formation  of  sulfuric  acid  from 
sulfur  trioxide  and  water  is  due  to  the  opening  up  of  one 
of  the  double  bonds  between  the  sulfur  and  one  of  the 
oxygen  atoms,  and  the  addition  of  the  water  as  hydrogen 
and  hydroxyl  to  this  opened  up  group. 


O2S=O     ->    O2S-0+H-OH     ->    O2S 


/OH 
\OH 


This  explanation  cannot  be  applied  to  the  mechanism  in- 
volved in  the  formation  of  the  tetrachlorplatinic  acid, 
H2PtCl4(OH)2. 

The  addition  of  hydrogen  chloride  to  sulfur  trioxide, 
becomes  analogous  to  the  addition  of  hydrogen  chloride  to 
platinic  chloride,  yielding  in  the  first  case,  chlorsulfonic 
acid,  HSO3C1,  and  in  the  second  case,  chlorplatinic  acid, 
H2PtCl6. 

The  addition  of  potassium  chloride  to  platinic  chloride 
to  form  potassium  chlorplatinate,  K2PtCle,  is  similar  to  the 
formation  of  potassium  sulfate  from  potassium  oxide  and 
sulfur  trioxide. 


44  CHEMICAL  REACTIONS. 

The  addition  of  ammonium  chloride  to  platinic  chloride 
to  form  ammonium  chlorplatinate,  (NH^PtCle,  is  similar 
to  the  reaction  between  chromium  trioxide  and  ammonium 
chloride  to  form  CrO3ClNH4  (Werner).  (It  is  impossible 
to  go  into  all  the  examples  which  may  be  given  along  these 
lines,  and  the  reader  is  referred  to  Werner's  book  for  more 
complete  information.) 

It  is  possible  to  formulate  the  reaction  involved  in  the 
formation  of  the  first  stage  addition  compound,  in  the  case 
of  many  of  these  substances  as  follows  : 

so3  +  H2Os^so3;:H2o,         so3 

S03  +  NH3*-^ 
PtCl4 

PtCl4 

PtCl4 


PtCU 

AuCl3 
AuCl3  + 


etc. 


These  primary  addition  products  may  then  rearrange  or 
tautomerize  into  the  structures  for  the  acids  or  salts  which 
have  already  been  given  and  which  represent  the  customary 
formulations. 

It  has  been  mentioned  that  addition  compounds  which 
consist  of  more  than  one  zone  are  ionogens  by  definition  or 
description,  and  that  if  the  components  in  one  zone  are 
hydrogen  or  hydrated  hydrogen,  the  compound  is  an  acid. 
The  hydrogen  bearing  this  relation  to  the  addition  com- 


ACIDS  AND  BASES.  45 

pound  corresponds  to  the  hydrogen  ion  of  Arrhenius.  A 
substance  dissolved  in  water  will  be  an  acid  (that  is,  it  will 
furnish  hydrogen  ion  H+)  if  it  forms  hydrates  containing 
hydrogen  or  hydrated  hydrogen  in  one  of  the  zones.  For 
example,  hydrogen  chloride  forms  hydrates  when  dissolved 
in  water  and  is  an  acid,  but  when  dissolved  in  some  solvent 
with  which  it  does  not  form  an  addition  compound,  a 
hydrocarbon  for  example,  then  it  does  not  have  the  proper- 
ties of  an  acid.  The  hydrate  of  hydrogen  chloride  in  dilute 
aqueous  solution  will  undoubtedly  have  a  great  number 
of  water  molecules  attached  to  it,  and  its  probable  structure 


may  be  expressed  as 


01    The  part  within 


the  brackets  is,  therefore,  an  example  of  hydrated  hydro- 
gen. 

Hydrogen  chloride  may  also  form  an  acid  by  combining 
with  other  compounds  than  water.  Thus  it  may  do  so  by 
reacting  with  either  platinic  chloride  to  form  chlorplatinic 
acid  or  by  displacing  water  in  tetrachlorplatinic  acid, 
H2PtCl4(OH)2,  and  thus  forming  chlorplatinic  acid.  In 
chlorplatinic  acid,  the  platinic  chloride  may  be  said  to  serve 
the  same  purpose  as  the  water  does  in  the  hydrate  of  hydro- 
gen chloride,  that  is,  it  separates  the  hydrogen  and  tlte 
chlorine  of  the  hydrogen  chloride  into  the  two  zones..  It- 
might  be  said,  therefore,  that  since  water  is  often  spoken  o£" 
as  an  ionizing  medium  for  electrolytes,  that  the  platim<* 
chloride  is  also  in  the  same  sense  an  ionizing  mediu^a  for 
certain  electrolytes  such  as  hydrogen  Chloride,,  potassium} 
chloride,  etc. 

Since  the  behavior  of  ammonia,  toward  hydrogen  chloride 
is  similar  to  that  of  water  and  of  plating  c&loride,  it  also 
should  yield  an  acid  in  forming  an.ajjppiopiate  with  hydrogen 
chloride.  This  is  in  fact  th$  ^e,,  Dor  wkea  ammonium 


46  CHEMICAL  REACTIONS. 

chloride  or  hydrogen  chloride  is  dissolved  in  liquid  ammonia 
and  this  solution  treated  with  magnesium  or  a  similar 
metal,  hydrogen  is  evolved,  and  the  metal  is  dissolved.  At 
the  present  time,  however,  it  is  not  customary  to  consider 
such  an  ammoniate  as  an  acid. 

Hydrogen  chloride  by  itself  is  not  an  acid,  but  becomes 
one  when  dissolved  in  water  by  virtue  of  the  formation  of 
hydrates.  In  the  same  way,  sulfur  trioxide  is  not  an  acid 
and  only  becomes  one  when  combined  with  some  compound 
containing  hydrogen,  such  as  water.  However,  sulfuric 
acid  is  more  closely  related  in  the  formulations  to  the  tetra- 
chlorplatinic  acid,  H2PtCl4(OH)2,  than  to  the  hydrate  of 
hydrogen  chloride.  The  sulfur  trioxide  and  the  platinic 
chloride  first  add  to  the  water  and  then  tautomerism  and 
shifting  of  the  hydrogen  to  the  outer  zone  takes  place. 
On  the  other  hand,  with  the  hydrate  of  hydrogen  chloride, 
the  water  first  adds  and  then  the  chlorine  enters  the  outer 
zone.  Sulfuric  acid,  H2SO4,  which  is  itself  an  addition 
compound,  may  add  to  water  to  form  compounds  of  the 
third  order  such  as  H2SO4H20;  H2SO4.2H2O.  The  con- 
stitution of  such  higher  hydrates  may  be  indicated  as  follows : 


It  therefore  becomes  evident  that  the  mono-hydrate, 
SO3.H2O,  will  have  the  constitutional  formula  H2(SO4)  and 
.be  similar  to  tetrachlorplatinic  acid  H2(PtCl4(OH)2),  while 
the  hydrates  of  the  higher  orders  will  have  hydrogen  in  the 
fiydrated  form,  and  correspond  to  the  hydrates  of  hydrogen 
chloride- 

The  structures  of  acids  as  outlined  are  not  complete  for 
the  co-ordination  number  of  the  hydrogen  has  not  been 
taken  into  account  in  their  development.  Unfortunately, 
the  co-ordination  number  of  hydrogen  is  not  known.  At 
;the  same  time,  it  has  not  been  established  experimentally 


ACIDS  AND   BASES. 


47 


whether  it  is  necessary  for  the  co-ordination  value  of  a 
central  atom  to  be  satisfied  before  ionization  will  take  place, 
or  in  other  words,  in  order  that  the  compound  shall  exist 
in  what  has  been  termed  inner  and  outer  zones.  As  far 
as  this  point  has  been  investigated,  as  for  platinum,  cobalt, 
and  chromium  compounds,  it  seems  as  if  the  co-ordination 
number  (maximum)  must  be  satisfied  before  ionization 
takes  place.  With  hydrogen  chloride  and  ammonia,  for 
example,  ammonium  chloride,  NH4C1,  would  not  be  an 
ionogen,  but  only  becomes  one  when  more  molecules  of 
ammonia  in  liquid  ammonia  solution,  or  water  molecules 
in  an  aqueous  solution  collect  about  the  hydrogen  atom 
until  the  co-ordination  value  is  reached.  If  the  co-ordina- 
tion number  of  hydrogen  is  assumed  to  be  four>  then  the 
formulas  for  ammonium  chloride  would  be 


/H20 


and 


non-ionogen 


or 
Cl 


^N 

H3 


•Cl 


These  formulas  involve  the  view  that  when  ammonium 
chloride  is  dissolved  in  water  it  undergoes  hydration. 

The  mechanism  of  the  ionization  of  hydrogen  chloride 
in  water  may  be  expressed  similarly.  The  water  molecules 
play  the  same  part  as  the  ammonia  forming  the  hydrate 


which  may  be  represented  as  follows: 


That  part  of  the  compound  within  the  brackets  or  inner 
zone  is  the  hydrated  hydrogen  ion.  Since  water  is  the 
common  solvent  for  most  electrolytes,  it  is  customary  when 
speaking  of  hydrated  ions  to  refer  to  the  central  atom  or 
group  acting  as  ion,  or  in  this  particular  case,  the  hydrated 
hydrogen  ion.  When  however  part  of  the  water  molecules 


48  CHEMICAL  REACTIONS. 

are  displaced  by  ammonia,  then  they  are  spoken  of  as 
ammonium  ion  and  not  hydrogen  (or  hydrated  hydrogen) 
ion.  The  similarity  is  further  emphasized  by  reactions 
such  as  the  solution  of  zinc  in  a  water  solution  of  ammonium 
chloride  or  the  solution  of  magnesium  in  a  liquid  ammonia 
solution  of  hydrogen  chloride  with  evolution  of  hydrogen, 
similar  to  the  solution  of  a  metal  in  an  aqueous  solution  of 
an  acid. 

It  further  emphasizes  the  point  that  ammonium  salts 
are  only  hydrogen  compounds  where  the  hydrogen  atom 
has  associated  with  one  ammonia,  while  if  it  has  associated 
with  it  more  ammonia  molecules  it  is  generally  considered 
as  an  abnormal  addition  compound.  Ammonium  salts  are 
only  one  particular  case  of  ammoniated  hydrogen  com- 
pounds. Similarly,  oxonium  salts  are  only  a  particular 
case  of  the  series  of  hydrates  of  hydrogen  and  similar 
compounds. 

It  is  also  possible  by  this  theory  to  correlate  the  fact  that 
platinic  chloride  dissolved  in  aqueous  hydrochloric  acid 
forms  chlorplatinic  acid  with  the  formation  of  addition 
compounds  similar  to  ammoniates.  Since  the  co-ordination 
number  of  the  platinum  atom  is  six,  the  platinic  chloride 
can  combine  with  two  molecules  of  hydrogen  chloride  to 
form  a  compound  similar  to  the  diammoniate.  Since, 
however,  the  addition  compound  exists  in  a  water  solution, 
the  hydrogen  chloride  can  also  form  the  hydrate  and  equal 
the  co-ordination  number  of  hydrogen.  In  this  case  the 
hydrogen  chloride  will  become  ionized  just  as  with  the 
ammonium  chloride  in  the  water  solution.  In  other  words, 
either  the  water  or  platinic  chloride  which  make  up  the  co- 
ordination value  of  the  hydrogen  of  the  hydrogen  chloride 
will  enter  between  the  hydrogen  and  the  chlorine  and 
Separate  or  ionize  them.  It  is  probable  that  in  this  case 
the  platinic  chloride  enters  between  the  hydrogen  and  the 
chlorine  and  hence  the  structural  formula  for  chlorplatinic 


ACIDS  AND   BASES.  49 

acid  may  be  written  as  follows — assuming  the  co-ordination 


Pt  Cle] 


number  of  hydrogen  to  be  four : 


It  is  to  be  noted  that  in  the  case  of  chlorplatinic  acid  the 
platinic  chloride  is  really  considered  to  be  the  ionizing 
agent  of  the  hydrogen  chloride,  while  in  the  case  of  the 
hydrate  of  hydrogen  chloride,  water  is  considered  to  be  the 
ionizing  agent.  Furthermore,  when  platinic  chloride  acts 
as  the  ionizing  agent  then  the  hydrogen  or  hydrated 
hydrogen  occurs  in  the  outer  zone  or  in  other  words  the 
separate  ion,  and  the  chlorine  in  the  inner  zone  or  the 
complex  ion  containing  the  platinum  atom.  When  am- 
monia or  water  acts  as  the  ionizing  agent  in  the  case  of 
ammonium  chloride  in  a  water  solution,  then  the  chlorine 
occurs  in  the  outer  zone  or  in  the  part  which  does  not  remain 
in  the  complex  ion.  If  the  valence  charges  upon  the  various 
atoms  in  these  addition  compounds  are  taken  into  account, 
it  also  becomes  evident  that  the  atom  with  the  same  charge 
as  that  of  the  atom  which  enters  in  between  the  two  atoms 
is  the  one  which  appears  in  the  outer  zone.  Thus  when  the 
ammonia  ionizes  the  hydrogen  chloride  the  nitrogen  is  the 
entering  atom  and  is  predominatingly  negative  and  there- 
fore the  chlorine  "would  be  in  the  other  zone,  while  when 
platinum  which  is  predominatingly  positive  is  the  entering 
atom,  then  the  hydrogen  which  is  positive  occurs  in  the 
other  zone  from  the  platinum  atom. 

It  has  already  been  pointed  out  that  hydrogen  chloride 
when  dissolved  in  water  acquires  the  properties  of  an  acid. 
In  the  form  of  its  hydrates  the  maximum  co-ordination 
number  of  the  hydrogen  is  probably  equalled  and  the  water 
entering  between  the  hydrogen  and  the  chlorine  of  the 


50  CHEMICAL  REACTIONS. 

hydrogen  chloride  causes  ionization,  which  is  indicated  in 


the  formula  by  two  zones 


When  pla- 


H2 

tinic  chloride  is  added  to  an  aqueous  solution  of  hydro- 
chloric acid,  or  hydrate  of  hydrogen  chloride,  the  di- 
basic acid  chlorplatinic  acid  is  formed,  generally  given  the 
formula  H^PtCle)  and  assigned  by  Werner  the  structure 


H2 


[Cl       Cl~| 
Cl  Pt  Cl     . 
Ol       C1J 


Here  again  the  co-ordination  number  of  hydrogen  will  be 
considered  as  well  as  that  of  platinum.  In  other  words, 
just  as  in  the  case  of  hydrogen  chloride  in  water,  the  sub- 
stance does  not  ionize  until  the  co-ordination  value  of  the 
hydrogen  is,  reached,  and  consequently  the  more  correct 
formulation  would  be  (H2O^)xH2[PtCl6].  The  part 
actually  played  by  the  platinic  chloride  in  forming  the 
chlorplatinic  acid  in  a  water  solution  of  hydrogen  chloride, 
is  that  platinic  chloride  replaces  the  ionizing  molecule  of 
water  in  the  hydrate  of  hydrochloric  acid. 


M 

^±)X  H-O-f- 


Cl  +  Pt 


It  is  interesting  to  note  the  frequency  of  the  occurrence 
of  complexes  in  the  inner  zone  in  which  the  co-ordination 
number  of  the  central  atom  is  eight.  H2(S04),  H(MnO4), 
H(C1O4),  H3(AsO4),  (RuO4),  (OsO4),  etc.,  all  conform  to 
the  general  type  (AO4)  for  the  inner  zone,  water  of  hydra- 
tion  being  omitted  in  these  formulas.  In  determining  the 
co-ordination  number  of  an  atom,  the  rule  is  followed  here 
that  a  univalent  atom  such  as  chlorine  and  a  compound 
such  as  hydrogen  chloride  counts  as  one,  while  a  bivalent 
atom  such  as  oxygen  counts  as  two.  This  rule  is  arbitrary. 


ACIDS  AND  BASES.  51 

For  the  present  it  is  necessary  to  have  some  such  rule  and 
collect  data.  It  will  undoubtedly  be  possible  in  the  future 
to  find  a  more  general  rule  and  method  of  determining  these 
capacity  numbers. 

It  was  stated  before  that  it  has  been  customary  to  assign 
the  hydroxyl  structure  to  sulfuric  lacid  and  its  hydrates. 

HO.      s$  H  O  OH  HO^^  ^OH 

SC  S-OH  HO  -  S—  -OH 

UO'     X)  HO^  ^0  HO^         ^OH 

SO3.H2O  S03.2H2O  S03.3H2O 

According  to  these  structures  the  double  linking  between 
the  oxygen  and  the  sulfur  opened  up  and  added  the  hydro- 
gen and  hydroxyl  of  the  water,  forming  in  this  way  two 
hydroxyl  groups  combined  with  the  sulfur  in  place  of  one 
oxygen 


Accordingly,  the  dihydrate  should  be  a  tetrabasic  acid  if 
the  acidity  were  due  to  the  hydrogen  of  the  hydroxyl,  but 
this  is  contrary  to  experimental  facts.  Similarly,  osmium 
and  ruthenium  oxides  might  be  expected  to  show  a  greater 
tendency  to  form  acids  than  sulfur  trioxide  since  they  con- 
tain more  oxygen  atoms  with  double  linking  to  combine 
with  the  water.  It  is  evident,  therefore,  that  a  knowledge 
of  the  co-ordination  number  as  well  as  of  the  atomic  valence 
is  necessary  in  order  to  determine  the  basicity  of  an  acid. 
Just  as  there  is  a  series  of  acids  in  which  the  co-ordination 
number  of  the  central  atom  is  eight,  a  series  of  acids  exists 
in  which  the  co-ordination  number  is  six.  An  example  of 
this  series  is  nitric  acid  H(NQ3).  The  atomic  valence  of 
the  nitrogen  is  plus  five,  the  co-ordination  number  six, 
and  the  basicity  one.  The  same  is  true  of  chloric  acid 
H(C1O3),  iodic  acid  H(IO3),  etc.  Meta-phosphoric  acid, 
H(PO3),  belongs  to  this  group,  although  ortho-phosphoric 


52  CHEMICAL  REACTIONS. 

acid,  H3PO4,  belongs  to  the  group  in  which  the  co-ordination 
number  is  eight.  This  brings  up  the  question  of  whether 
an  acid,  the  co-ordination  number  of  whose  central  atom  is 
six,  can  be  converted  into  one  whose  central  atom  has  a 
co-ordination  number  of  eight  by  means  of  hydra tion. 
This  appears  to  be  possible,  for  example,  in  passing  from 
metaphosphoric  acid  to  the  ortho  acid.  On  the  other  hand, 
nitric  acid,  and  the  nitrates  of  the  alkali  metals,  form  hy- 
drates, but  only  mono-basic  nitric  acid  has  been  observed 
experimentally.  The  additional  molecules  of  water  in  the 
hydrates  of  nitric  acid  may,  therefore,  be  combined  with 
the  hydrogen  atom  which  would  act  as  a  second  central 
atom,  or  be  combined  with  the  nitrogen  in  such  a  way  as 
not  to  tautomerize  the  hydrogen  of  these  water  molecules 
into  the  outer  zone,  or  they  may  be  added  to  the  double 
linking  between  the  oxygen  and  nitrogen  and  be  present 
as  hydroxyl  groups. 


/0H 

N 


[NO3J    or      H[N03-^=-(H2O)]     or    H 

V 

The  co-ordination  number  is  a  function  of  external 
physical  conditions.  Its  value  in  the  case  of  the  nitrogen 
in  nitric  acid  is  six  in  all  the  conditions  under  which  nitrates 
have  been  studied.  With  the  acids  of  phosphorus,  however, 
the  co-ordination  number  may  change  from  six  to  eight. 
This  change  is  similar  to  the  changes  which  occur  with 
atomic  valence.  Some  elements  can  show  several  different 
states  of  valence,  while  others  show  only  one. 

The  ionic  theory  showed  that  bases  yield  hydroxyl  ions 
in  aqueous  solution,  and  that  a  base  might  be  defined  as  a 
substance  which  in  solution  forms  hydroxyl  ions. 

Since  ammonium  salts  can  be  formed  directly  by  the 
addition  of  ammonia  and  acid  to  each  other,  ammonia 
itself  has  sometimes  been  spoken  of  as  a  base.  Similarly, 
since  amines  are  like  ammonia  in  this  respect,  they  also 


ACIDS  AND  BASES.  53 

have  been  considered  to  be  bases.  At  first,  in  order  to 
distinguish  them  from  the  true  metallic  alkalies,  they  were 
sometimes  called  alkaloids  (A.  W.  Hofmann,  Lieb.  Ann. 
73,  91  (1850)).  This  term,  however,  is  now  reserved  for 
the  more  complicated  amines  which  occur  in  nature,  which 
show  marked  physiological  properties.  Two  different  defi- 
nitions for  the  term  base  have  been  current  with  the  amines. 
(1)  They  furnish  hydroxide  ion  in  aqueous  solution.  (2) 
They  combine  with  acids  to  form  substituted  ammonium 
salts.  This,  naturally,  has  led  to  some  confusion,  since 
amines  have  frequently  been  called  strong  bases  or  weak 
bases,  depending  upon  the  amount  to  which  ammonium 
salts  were  formed  when  they  were  added  to  an  acid. 

According  to  the  ionic  theory,  the  relative  strengths  of 
different  bases  are  given  by  the  ionization  constants  as 
calculated  from  the  Ostwald  dilution  law,  these  depending 
upon  the  concentrations  of  ionized  and  un-ionized  sub- 
stances present  in  solution.  The  equation  for  calculating 
the  ionization  constant  (which  naturally  should  hold  for 
all  substances  in  solution,  not  merely  bases)  is  as  follows 
for  a  substance  BA,  ionizing  into  B+  and  A~: 

+~ 


[BA] 

in  which  the  terms  in  brackets  denote  the  concentrations. 
Highly  ionized  substances,  including  the  bases  sodium 
and  potassium  hydroxides,  etc.,  give  values  for  the  ioniza- 
tion constants  which  vary  with  the  concentration.  On  the 
other  hand,  slightly  ionized  bases,  among  which  may  be 
included  some  of  the  substituted  ammonium  hydroxides, 
give  constant  values,  and  it  appears  as  if  the  strengths  of 
these  bases  might  be  compared  in  this  way.  A  difficulty 
arises,  however,  which  prevents  a  direct  comparison.  Dis- 
tribution experiments  with  organic  solvents  and  an  aqueous 
solution  of  ammonia,  showed  that  in  the  water  only  a  part 


54  CHEMICAL  REACTIONS. 

of  the  latter  was  present  as  ammonium  hydroxide,  the  rest 
being  dissolved  as  such  (ammonia)  or  more  probably  as  a 
hydrate.  The  ionization  constant,  to  show  the  strength 
of  the  base  should  be  calculated  from  the  concentration  of 
the  ammonium  hydroxide  from  the  equation 

[NHi+KOH-] 
[NH4OH] 

At  the  same  time,  the  equilibrium 

[NH3][H20]  _ 
[NH4OH] 

or  some  similar  equilibrium,  must  be  taken  into  account. 
The  same  is  true  for  the  substituted  ammonium  hydroxides. 
The  values  of  the  ionization  constants  for  these  bases,  as 
determined  ordinarily,  are  apt  to  be  misleading  for  this 
reason.  A  few  of  the  values  h^ve  been  determined  cor- 
rectly. The  influence  of  the  solvent  is  shown  here,  but  a 
satisfactory  interpretation  of  its  action  in  the  ionization  of 
these  bases  and  of  other  bases  is  not  given  in  the  ionic 
theory.  The  further  developments,  just  as  with  the  acids, 
follow  the  lines  indicated  by  Werner  and  the  conceptions 
developed  here. 

According  to  Werner  (Neuere  Anschauungen,  pp.  268- 
270),  an  anhydro  base  is  a  substance  which  forms  a  hydrate 
with  water  and  then  yields  hydroxide  ion  and  a  complex 
positive  ion  in  aqueous  solution.  The  anhydro  base 
ionizes  in  this  way  by  combining  with  the  hydrogen  ion  of 
the  water,  and  producing  hydroxide  ions  (from  the  water) 
in  a  concentration  characteristic  for  the  substance.  Aquo 
bases,  or  bases,  are  addition  compounds  of  substances  with 
water  which  yield  hydroxide  ions  in  aqueous  solution. 
The  method  of  indicating  these  relations  with  hydroxyl 
in  the  outer  zone,  etc.,  follows  from  what  has  been  said 
before.  The  introduction  of  the  electron  conception  of 
valence  shows  the  distribution  of  the  charges,  etc.  It  will 
not  be  necessary  to  develop  these  relations  further  here- 


ACIDS  AND  BASES.  55 

The  statement  is  sometimes  made  that  tetramethyl 
ammonium  hydroxide  is  so  strong  a  base  that  neither 
sodium  nor  potassium  hydroxide  can  separate  it  from  its 
salts,  but  that  silver  hydroxide  must  be  used  for  this 
purpose.  It  is  much  more  probable  that  the  reason  for 
the  silver  hydroxide  being  much  more  efficient  than  the 
alkali  hydroxide  is  the  low  solubility  of  the  silver  halide 
usually  formed  as  one  of  the  dissociation  products  of  the 
intermediate  addition  compound.  In  place  of  using  silver 
hydroxide,  the  same  reaction  may  be  brought  about  by 
allowing  the  reaction  to  take  place  in  some  other  solvent 
such  as  alcohol.  This  is  a  way  of  changing  the  external 
physical  conditions  so  as  to  favor  the  dissociation  of  the 
intermediate  addition  compound  in  the  desired  direction 
as  will  be  explained  in  later  chapters,  because  of  the  smaller 
solubility  of  the  sodium  or  potassium  chloride  in  alcohol. 

The  state  of  substances  in  solution  will  now  be  taken  up 
briefly.  The  electrolytic  dissociation  of  a  large  number  of 
substances  is  dependent  evidently  upon  the  properties  of 
the  solvent  as  well  as  upon  the  character  of  the  dissolved 
substance  (solute),  because  on  the  one  hand  all  substances 
do  not  ionize  in  a  solvent  such  as  water,  and  on  the  other 
hand,  a  substance  may  ionize  in  one  solvent,  hydrogen 
chloride  in  water,  and  not  in  a  different  solvent,  hydrogen 
chloride  in  benzene.  The  solvent  must,  therefore,  also 
be  considered  in  the  ionization  relationships  and  the  manner 
In  which  it  may  be  done  follows  directly  from  what  has 
ibeen  said. 

As  pointed  out,  hydrogen  chloride  in  itself  is  not  an  acid, 
but  only  becomes  one  when  it  forms  a  compound  of  a 
higher  order,  or  in  other  words,  an  addition  compound. 
Hydrogen  chloride  is  able  to  form  compounds  of  higher 
orders  with  the  compounds  of  the  first  order,  ammonia, 
platinic  chloride,  sulfur  trioxide,  auric  chloride,  water,  etc., 
.the  compounds  of  the  second  order  which  are  formed  being 
.5 


56  CHEMICAL  REACTIONS. 

formulated  as  follows:  [HNH3]C1,  H2[PtCl6],  H[SO3C1], 
H[AuCl4],  [H2OH]C1,  etc.  The  linkings  between  the  indi- 
vidual atoms,  however,  follow  the  principles  outlined  in  the 
first  chapter,  the  division  of  the  compounds  into  zones  as  a 
rule  not  influencing  the  distribution  of  the  electric  charges 
due  to  the  combinations  between  the  atoms,  except  for 
some  cases  of  intramolecular  oxidation  and  reduction. 

The  last  of  the  compounds  given  in  the  preceding  para- 
graph was  [H2OH]C1.  This  compound  with  water  would 
evidently  be  an  example  of  the  compounds  formed  when 
hydrogen  chloride  is  dissolved  in  water.  Many  substances 
combine  with  water  to  form  compounds  containing  water 
of  crystallization.  In  the  last  fifteen  years  much  evidence 
has  been  accumulated  which  shows  that  hydrates  exist  in 
solution  as  well,  and  also  that  ions  are  hydrated.  The 
most  careful  work  in  this  field  was  done  by  E.  W.  Washburn 
and  by  G.  Buchbock,  the  former  studying  the  relative 
hydration  of  the  positive  and  negative  ions  of  the  chlorides 
of  lithium,  sodium,  potassium,  and  caesium,  and  the  latter 
of  hydrochloric  acid.  That  is  to  say,  they  determined  the 
ratio  between  the  number  of  water  molecules  combined 
with  the  lithium,  sodium,  potassium,  caesium,  or  hydrogen 
ion,  and  the  number  of  water  molecules  combined  with  the 
negative  chlorine  ion  for  certain  definite  concentrations  of 
aqueous  solutions  of  these  salts.  Different  amounts  of  water 
were  found  to  be  combined  with  the  positive  ions,  but  in  every 
case,  more  water  was  combined  with  or  associated  with, 
the  positive  ion  than  with  the  negative  ion.  It  was  im- 
possible to  determine  directly  whether  any  water  was  asso- 
ciated with  the  negative  ion,  since  the  method  permitted 
only  of  the  determination  of  the  relative  extents  of  hydra- 
tion. 

The  existence  of  hydrated  ions  rests  therefore  upon  a  firm 
experimental  basis.  The  formula  for  the  compound  hydro- 
gen chloride  with  water  was  given  as  [H2OH]C1.  In  detail 


ACIDS  AND  BASES. 


57 


this  would  be 


H 


m  wnicn  the  oxygen  is  in  the 


onium  state  with  a  valence  of  —  3  +  1  =  —  2.  The  pre- 
dominatingly negative  oxygen  holds  the  positive  hydrogen 
in  the  Inner  zone  and  the  negative  chlorine  in  the  outer 
zone,  and  the  ions  are  [H30]+  and  Cl~,  omitting  the  addi- 
tional water  molecules  which  may  be  combined  with  the 
hydrogen  and  the  chlorine. 

It  is  necessary  to  mention  here  the  fact  that  water  may 
also  be  in  combination  with,  or  associated  with  the  negative 
ion,  as  well  as  with  the  positive  ion.  A  salt  such  as  hydrated 
magnesium  sulfate  will  illustrate  this.  The  composition  of 
this  substance  is  MgSO4.7H2O.  It  has  been  shown  by  vapor 
tension  measurements  that  six  of  the  water  molecules  bear 
the  same  relation  to  the  molecule  as  a  whole,  but  different 
from  the  seventh  molecule.  Furthermore,  the  study  of  the 
optical  activity  (rotation  of  the  plane  of  polarized  light)  of 
the  substance,  indicates  that  one  molecule  of  water  is 
associated  with  the  SO4  group.  This  indicates  that  the 
water  may  be  present  in  combination  with  either  of  the 
two  parts  of  the  molecule  which  form  the  ions,  or  that  both 
positive  and  negative  ions  may  be  hydrated. 

It  was  shown  previously  that  hydrates  and  ammoniates 
belong  to  the  class  of  addition  compounds.  The  substance 
CrCl3.6H2O,  for  example,  is  similar  in  structure  to  the 
substance  PtCU.GNHs,  etc.  The  water  in  these  compounds 
is  in  combination  with  the  metallic  atom  in  the  inner  zone 
or  sphere,  where  the  latter  functions  as  the  central  atom. 
The  structures  of  some  of  these  compounds  may  therefore 
be  given  as  follows  : 


>^-Cl 
L2 

4ci 

Cl 


>^4C1 
•Cl 


-Cl 


+   6 


Cr  C13.6H2O 


Al  C1.6H0 


Ca  C12.6H2O 


Cl 
CJ 


58  CHEMICAL  REACTIONS. 

It  was  pointed  out  that  the  co-ordination  number  of 
the  central  atom  varied,  depending  upon  certain  physical 
conditions  such  as  temperature,  etc.  This  means  that  the 
number  of  molecules  of  water  in  the  hydrated  salts  varies 
with  the  conditions,  but  there  are  certain  limits  within 
which  a  hydrated  salt  having  a  perfectly  definite  composi- 
tion is  stable.  A  study  of  these  substances  from  the  point 
of  view  of  the  phase  rule  shows  the  compositions  and  ranges 
of  stability  of  the  various  hydrates  and  other  compounds. 
For  calcium  chloride,  the  forms  which  are  known  include 
CaCl2,  CaCl2.2H2O,  CaCl2.4H2O,  and  CaCl2.6H2O.  The 
graphic  formulas  for  these  substances  might  be  written 
as  follows: 


=CaC 


OH2 


Cl 


Ca  C12  Ca  C12.2H20        Ca  C12.4H2O  Ca  C12.6H2O 

Several  relations  are  brought  out  by  these  formulas 
In  the  first  place,  the  calcium  is  taken  to  be  in  the  same 
state  of  oxidation  (+  2)  in  all  the  compounds.  In  the 
second  place,  according  to  these  formulas,  the  only  sub- 
stance which  would  ionize  in  solution  is  the  last  which 
would  form  the  ions  [Ca.6H20]++  and  2C1.  At  present 
there  is  no  experimental  evidence  available  to  test  this 
question,  and  the  reason  for  writing  the  formulas  in  this 
way  and  indicating  this  fact  is  that  with  similar  compounds, 
such  as  the  hydrates  of  chromic  chloride  and  the  am- 
moniates  of  platinic  chloride,  the  chlorine  only  appears  in 
the  outer  zone  and  forms  ions  when  the  final  hexahydrate 
or  hexammine  stage  is  reached.  For  this  reason  the  di- 
and  tetrahydrates  are  formulated  as  non-ionogens. 

It  has  been  possible  so  far  to  assign  definite  structural 
formulas  to  many  of  the  compounds  which  are  made  up  of 
two  or  more  simpler  molecules  (compounds  of  the  second 


ACIDS  AND  BASES.  59 

and  higher  orders).  The  formulas  assigned  have  been 
based  upon  certain  definite  chemical  and  physical  reactions 
or  relations.  The  compounds  have  a  fairly  considerable 
range  of  stability  so  that  the  study  of  their  reactions  makes 
it  possible  to  treat  of  a  portion  of  the  molecule  at  a  time, 
leaving  the  remainder  constant  or  unchanged.  In  develop- 
ing the  subject,  it  is  now  necessary  to  take  up  more  complex 
substances;  that  is  to  say,  the  compounds  of  the  second, 
third,  etc.,  order,  or  the  binary,  ternary,  etc.,  compounds. 
These  compounds  of  higher  orders  are  made  up  of  com- 
pounds of  the  first  order,  and  must  be  considered  in  the 
same  way  as  far  as  possible.  A  difficulty  is  encountered 
in  the  practical  treatment.  That  definite  compounds  are 
formed  may  be  proved  conclusively  in  many  of  these 
binary  or  ternary  mixtures,  but  the  linkings  between  the 
atoms  cannot  be  determined  as  definitely.  The  methods  in 
use  for  determining  the  graphic  formulas  cannot  be  applied 
to  these  more  complex  substances,  partly  because  of  their 
ready  dissociation  into  their  constituent  molecules,  partly 
because  of  the  internal  rearrangements  which  take  place 
readily,  and  perhaps  for  other  reasons.  The  difficulty  of 
assigning  definite  structural  formulas  to  a  number  of  these 
substances  must  be  faced  squarely.  An  attempt  to  write 
the  formulas  with  insufficient  evidence  is  of  no  value,  but 
on  the  other  hand  it  is  possible  to  use  the  classifications 
involving  these  compounds  of  higher  orders  without  assign- 
ing graphic  formulas  to  them.  In  a  way  this  appears  to 
go  no  further  than  to  designate  these  compounds  as  molecu- 
lar compounds,  but  it  will  be  shown  in  succeeding  chapters 
how  different  classes  of  reactions  may  be  grouped  together 
so  that  even  without  the  use  of  all  the  linkings  between  the 
atoms,  light  will  be  thrown  upon  the  mechanism  of  a 
number  of  reactions.  This  is  true  especially  when  the 
distribution  of  the  charges  on  the  atoms  constituting  the 
molecules  is  taken  into  account. 


CHAPTER  IV. 
CATALYSIS. 

THE  conceptions  upon  which  the  structures  of  molecules 
are  based  have  been  elaborated  in  the  preceding  chapters. 
The  next  step  to  be  taken  involves  the  changes  which  may 
take  place  when  two  or  more  molecules  interact.  This 
would  include  changes  which  take  place  in  chemical  re- 
actions and  an  attempt  will  be  made  to  outline  a  general 
theory  of  chemical  reactions  from  the  standpoint  of  struc- 
tural chemistry  in  this  and  the  following  chapters. 

In  considering  such  a  general  theory  of  chemical  reactions, 
it  is  desirable  to  proceed  from  simple  to  more  complex 
phenomena.  In  order  to  lead  up  to  chemical  reactions  in 
general,  catalytic  reactions  will  first  be  taken  up  as  simple 
examples.  This  apparently  reverses  the  customary  order 
of  treatment,  but  a  short  discussion  of  catalysis  as  it  is 
ordinarily  presented  and  as  it  will  be  presented  here  will 
serve  to  show  the  relations. 

A  catalytic  action  is  generally  defined  as  one  in  which  the 
velocity  of  a  reaction  is  modified  by  the  presence  of  a  sub- 
stance which  is  itself  unchanged  at  the  end  of  the  reaction. 
The  substance  which  causes  such  an  action  is  called  the 
catalytic  agent  or  catalyst.  The  following  general  relations 
have  heretofore  been  assumed  to  apply  to  catalytic  actions. 

In  the  first  place,  the  catalyst  has  the  same  chemical 
composition  at  the  beginning  and  at  the  end  of  the  re- 
action. A  small  amount  of  the  catalyst  is  able  to  effect 
the  transformation  of  a  large  amount  of  the  reacting  sub- 
stance. A  catalyst  can  only  modify  the  velocity  of  a 
reaction,  it  is  incapable  of  starting  a  reaction.  A  catalytic 
agent  does  not  affect  the  final  state  of  equilibrium  of  a 
reaction,  or,  in  other  words,  the  velocities  of  two  opposing 

60 


CATALYSIS.  61 

reactions  are  affected  to  the  same  extent  by  the  catalyst. 
The  state  of  equilibrium  is  independent  of  the  nature  and 
quantity  of  the  catalytic  agent. 

These  general  relations  have  been  taken  to  hold  for 
catalytic  actions  as  a  result  of  the  description  of  various 
reactions.  They  are  therefore,  used  as  definitions  of  cata- 
lytic reactions.  If,  by  definition,  a  reaction  follows  these 
laws,  it  is  catalytic,  otherwise  it  is  not.  While  it  is  neces- 
sary for  purposes  of  classification,  to  have  some  definitions 
of  this  kind,  the  way  in  which  the  classification  of  catalytic 
reactions  developed,  that  is,  very  often  by  the  introduction 
of  the  term  catalyst  when  unknown  factors  were  involved, 
has  confused  the  relation  of  these  reactions  to  chemical 
reactions  in  general. 

In  place  of  the  relations  pointed  out,  a  catalytic  action 
will  be  taken  to  be  based  upon  the  definition  of  a  catalyst 
as  a  substance  which  may  modify  the  velocity  of  a  reaction 
without  itself  undergoing  a  change  in  chemical  composition. 
No  further  limitations  will  be  introduced,  and  it  will  be 
shown  how  the  conclusions  from  this  point  of  view  compare 
with  the  conclusions  derived  from  or  based  upon  the  descrip- 
tion of  catalytic  reactions  used  heretofore.  The  definition 
given  when  used  with  the  general  equation  of  a  chemical 
reaction  evidently  simplifies  it  from  the  structural  or  com- 
positional point  of  view,  because  the  chemical  composition 
of  one  of  the  initial  and  final  products  of  the  reaction  is  the 
same.  The  way  in  which  such  a  substance  may  modify 
the  velocity  of  a  reaction  must  next  be  considered,  and  it  is 
this  point  which  forms  the  crux  of  the  general  theory  to  be 
used.  The  general  theory  consists  of  what  has  been  called 
the  "addition  theory"  of  chemical  reactions. 

In  considering  the  mechanism  of  chemical  reactions,  this 
theory  states  that  primary  addition  is  involved  in  chemical 
reactions  between  molecules  even  when  the  final  products 
obtained  indicate  substitution  or  other  change.  It  repre- 


62  CHEMICAL   REACTIONS. 

sents  the  most  general  case  of  chemical  reactions.  Evidence 
for  an  explanation  for  a  number  of  reactions  on  this  basis 
and  the  view  that  it  was  of  general  application  was  pre- 
sented some  years  ago  in  a  short  paper  (K.  G.  Falk  and 
J.  M.  Nelson,  Jour.  Amer.  Chem.  Soc.  37,  1732  (1915)). 
Catalytic  reactions  will  be  taken  up  as  a  group  of  addition 
reactions  following  the  same  laws  as  other  chemical  re- 
actions, with  one  condition  fixed,  namely,  that  one  of  the 
original  substances  which  takes  part  in  the  reaction  also 
appears  as  one  of  the  products  of  the  reaction.  The  com- 
plete change  may  be  represented  by  an  equation  of  the  form, 


in  which  the  substance  typified  by  D  acts  as  the  catalyst. 
A  reaction  such  as  this  may  be  considered  to  proceed  by  an 
addition  compound  being  formed  by  the  reacting  com- 
ponents with  the  catalyst,  and  this  complex  compound  then 
reacts  further  to  reform  the  catalyst  and  one  or  more  new 
molecules.  The  proviso  for  a  reaction  to  be  considered 
catalytic  is  that  one  of  the  substances  going  to  make  up  the 
addition  product  is  formed  again  when  the  addition  product 
breaks  down  or  reacts  further.  This  substance,  the  cata- 
lyst, which  has  gone  through  a  cycle  of  changes  and  has 
returned  to  its  original  condition,  is  evidently  able  to  go 
through  the  cycle  of  changes  again  with  fresh  material. 
The  action  of  the  catalytic  substance,  as  outlined,  may 
result  in  an  acceleration  of  the  changes  taking  place  in  the 
other  substances  present,  a  retardation,  or  finally  show  no 
effect  on  the  velocity  of  the  reaction.  If  a  retardation 
would  result  when  the  catalyst  takes  part  in  the  reaction, 
then,  since  reactions  would  be  taking  place  simultaneously 
without  and  with  the  catalytic  substance  as  part  of  the 
intermediate  addition  compound,  the  net  result  observed 
with  regard  to  the  velocity  would  be  that  in  which  the 
catalytic  substance  was  not  involved  unless  the  latter 


CATALYSIS.  63 

were  present  in  more  than  a  very  small  quantity.  The 
experimental  evidence  directly  in  favor  of  the  view  of  the 
production  of  addition  compounds  in  a  number  of  catalytic 
reactions  will  be  considered  next  and  then  some  theoretical 
developments  will  be  given. 

In  the  lead  chamber  process  for  the  manufacture  of 
sulfuric  acid,  nitric  oxide,  oxygen  (from  the  air),  sulfur 
dioxide,  and  water  (steam),  interact.  The  nitric  oxide 
acts  as  the  catalyst,  and  is  present  at  the  end  of  the  action, 
with  the  sulfuric  acid.  It  acts  as  "oxygen  carrier."  One 
of  the  intermediate  compounds  which  is  formed  contains 
nitrogen  peroxide  (NCfe),  sulfur  dioxide,  and  water.  It 
may  be  obtained  in  crystalline  form,  known  as  "chamber 
crystals"  which  have  the  composition  HSOaNC^,  nitro- 
sulfonic  acid,  under  certain  conditions.  This  substance  is 
decomposed  in  the  presence  of  an  excess  of  steam  or  water 
vapor  into  sulfuric  acid  and  nitric  oxide,  or  better,  nitrogen 
trioxide,  N203.  While  the  exact  formulation  of  the  inter- 
mediate compounds  is  not  simple  under  the  various  condi- 
tions, the  evidence  at  hand  is  sufficient  to  make  the  existence 
of  at  least  one  intermediate  compound  certain. 

The  reaction  between  an  alcohol  and  an  acid  to  form  an 
ester,  catalyzed  by  the  addition  of  acid,  takes  place  with 
the  formation  of  a  complex  intermediate  compound  con- 
taining the  catalyst  as  a  constituent.  The  evidence  for  this 
and  a  more  complete  discussion  of  this  reaction  will  be 
presented  in  Chapter  6.  The  existence  of  such  intermediate 
compounds  is  only  referred  to  here,  because  they  have  been 
shown  definitely  to  exist  in  a  number  of  cases. 

In  the  formation  of  ether  and  water,  or  of  ethylene  and 
water  from  alcohol  and  sulfuric  acid,  or  the  reverse  reactions, 
sulfuric  acid  plays  the  part  of  the  catalyst,  and  the  inter- 
mediate addition  compound  may  be  represented  by  alkyl 
sulfuric  acid,  RSC^H,  or  a  hydrate  of  it. 

Similarly  in  the  formation  of  ethylene  and  water  from 


64  CHEMICAL  REACTIONS. 

ethyl  alcohol,  zinc  chloride  acts  as  catalyst,  and  the  inter- 
mediate compound  is  represented  by  the  formula  ZnC^.- 
C2H5OH. 

Condensation  reactions  with  aluminium  chloride  as 
catalyst  also  involve  the  formation  of  intermediate  complex 
compounds  which  have  been  isolated  in  some  cases.  These 
will  be  taken  up  in  detail  in  Chapter  VII. 

The  catalytic  reactions  which  have  been  quoted  give 
direct  experimental  evidence  of  the  existence  of  intermediate 
compounds  of  the  reacting  substances  with  the  catalyst. 
The  list  as  given  is  not  complete,  by  any  means,  and  a 
study  of  the  scientific  and  patent  literature  of  the  past  few 
years  will  show  many  more  reactions  of  this  kind.  P. 
Sabatier,  in  his  book  "La  Catalyse  en  Chimie  Organi- 
que,"  1913,  assumed  the  formation  of  an  intermediate 
compound  of  catalyst  with  reacting  substances  in  all 
catalytic  reactions.  The  fact  that  intermediate  compounds 
have  been  isolated  shows  that  a  capacity  for  combination, 
or,  in  other  words,  an  unsaturation,  is  present  in  the  reacting 
substances.  This  unsaturation  may  depend  upon  a  definite 
atom  of  each  molecule,  or  upon  a  group  of  atoms  combined 
in  such  a  way  as  to  show  unsaturation  of  two  or  more  atoms 
(as,  for  example,  with  two  carbon  atoms  united  by  a  double 
linking  or  two  units  of  valence),  but  in  all  cases,  the  impor- 
tant feature  at  present  is  the  property  of  unsaturation  in 
connection  with  the  formation  of  the  intermediate  com- 
pound. 

The  fact  that  intermediate  complex  compounds  have 
been  isolated  in  a  number  of  catalytic  reactions,  naturally 
does  not  prove  that  they  are  formed  (with  the  catalyst) 
in  all  such  cases.  Some  evidence  will  now  be  presented  to 
indicate  that  unsaturation  of  certain  molecules  plays  an 
important  part  in  catalytic  reactions  which  apparently  do 
not,  at  first  sight,  fall  into  the  classification. 

It  has  been  known  for  some  time  that  a  given  reaction 


CATALYSIS. 


65 


may  proceed  faster  in  one  solvent  than  in  another.  As  an 
example,  the  reaction  between  triethylamine  and  ethyl 
iodide  in  which  tetraethylammonium  iodide  is  formed,  and 
for  which  the  rate  in  different  solvents  was  studied  by  N. 
Menschutkin,  may  be  quoted.  Menschutkin  mixed  one 
volume  of  equimolecular  amounts  of  the  reacting  substances 
with  fifteen  volumes  of  the  solvent,  and  heated  the  mixtures 
in  sealed  glass  tubes  at  100°  for  definite  periods  of  time. 

Velocity  of  Combination  of  Triethylamine  with  Ethyl  Iodide  in  Various 

Solvents. 


Velocity 

Constants. 

Ratios. 

Hydrocarbons. 
Hexane  CeHn        

0.000180 
0.000235 
0.00287 
0.00584 

0.00540 
0.0231 
0.0270 
0.1129 

0.000630 
0.000757 
0.0212 
0.0403 

0.00577 
0.0223 
0.0259 

0.0258 
0.0366 
0.0433 
0.0516 
0.133 

0.0608 
0.0889 
0.1294 

1 

1.3 
15.9 

38.2 

30 

128 
150 
627 

3.5 
4.2 
117.7 
223.9 

32.1 
123.9 
143.9 

143.3 
203.3 
240.5 
286.6 
742.2 

337.7 
493.9 

718.7 

0.13 
0.17 
2.2 
4.4 

4.0 
17.4 
20.3 
84.9 

0.47 
0.57 
16.0 
.     30.3 

4.3 
16.7 
19.4 

19.4 
27.5 
32.5 
38.0 
100.0 

45.7 
66.9 
97.3 

Heptane  CyHie        

Xylene  C6H4(CH3)2      

Benzene  CeHe        

Halogen  compounds. 
Propylchloride  C3H7C1 

Phenylchloride  C6H5C1 

Phenyl  bromide  C6H5Br 

a.  Bromnaphthalene  Ci0H7Br  

Simple  Ethers. 
Ethyl  isoamyl  ether  C2H5OC5Hii  
Ethyl  ether  C2H5OC2H5 

Phenetol  C2H5OC6H5  

Anisol  CH3OC6H5 

Esters. 
Isobutyl  acetate  C4H9.O.CO.CH3      .  .  . 

Ethyl  acetate  C2H5O.CO.CH3  

Ethyl  benzoate  C2H5O.CO.C6H5  

Alcohols. 
Isobutyl  alcohol  C4H9.OH  

Ethyl  alcohol  C2H5.OH  

Allyl  alcohol  C3H5.OH  

Methyl  alcohol  CH3.OH  

Benzyl  alcohol  C6H6.CH2.OH  

Ketones. 
Acetone  CH3.C(XCH3  

Acetone  (14.5  vol.)  +  Water  (0.5  vol.)  .  . 
Acetophenone  CH3.CO.C6H5  

66  CHEMICAL  REACTIONS. 

The  determination  of  the  amounts  of  tetraethylammonium 
iodide  formed,  enabled  him  to  calculate  the  velocity  con- 
stants for  the  reaction  using  the  equation  for  a  bimolecular 
reaction.  Some  of  these  values  (&)  for  the  reaction  in  differ- 
ent solvents  are  given  in  the  accompanying  table  [Z.  physik. 
Chem.  6,  43  (1890)].  The  ratios  given  in  the  last  two 
columns  show  the  relative  rates  of  reaction,  first  when  com- 
pared to  the  slowest  reaction,  whose  velocity  is  placed  equal 
to  one,  and  second,  on  the  basis  of  the  most  rapid  reaction 
which  is  placed  equal  to  100. 

The  results  given  in  this  table  do  not  indicate  clearly 
that  the  velocity  is  directly  connected  with  the  unsaturation 
as  ordinarily  considered.  Roughly  it  is  so,  and  if  certain 
solvents  are  omitted,  this  relation  is  very  nearly  true.  For 
the  present,  it  may  be  stated  that  the  unsaturation  is 
important  in  that  it  shows  the  capacity  to  form  addition 
products,  but  that  in  some  of  the  solvents,  polymerization 
of  the  solvent  molecules  themselves  occurs.  The  un- 
saturation shows  itself  in  two  ways,  as  polymerization  and 
as  formation  of  complex  molecules  with  other  substances, 
and  the  action  of  the  solvent  is  determined  by  these  two 
factors  and  their  relative  predominance. 

It  may  be  said  for  the  present,  therefore,  that  a  rough 
parallelism  between  the  unsaturation  of  the  solvent  and 
the  magnitude  of  the  velocity  constants  for  this  reaction 
exists. 

Unsaturation  may  therefore  be  used  as  the  property 
upon  which  the  catalysis  of  these  reactions  depend.  With- 
out entering  into  the  structural  formulas  of  the  addition 
products  at  present,  this  property  means  that  addition 
compound  formation  of  one  or  all  of  the  reacting  substances 
with  the  catalyst  precedes  or  accompanies  the  reactions. 
D.  Klein  [Jour.  Phys.  Chem.  15,  I  (1911)]  in  studying  the 
relative  rates  of  the  reaction  between  hydrogen  sulfide 
and  sulfur  dioxide  in  a  number  of  organic  substances, 


CATALYSIS.  67 

accounted  for  the  results  obtained  by  the  assumption  of 
intermediate  compounds  involving  the  reacting  compounds 
and  the  solvents  as  catalysts.  The  evidence  in  other  re- 
actions is  also  strong  enough  to  have  caused  a  number  of 
workers  to  assume  the  existence  of  such  intermediate 
products,  without  actually  having  isolated  them.  Some  of 
these  reactions  are  given  by  J.  W.  Mellor  in  his  "  Chemical 
Statics  and  Dynamics." 

The  theoretical  views  of  E.  C.  C.  Baly,  based  upon  the 
absorption  in  the  ultraviolet  region  of  the  spectrum  of  the 
reacting  substances,  before,  during,  and  after  the  reaction, 
and  outlined  in  Chapter  II  may  be  referred  to  in  this 
connection. 

A  group  of  catalytic  agents  which  is  continually  increasing 
in  importance  is  included  under  the  general  term  of  enzymes, 
the  catalysts  produced  by  living  organisms  and  which  are 
of  the  greatest  significance  in  all  life  processes.  Within 
recent  years  there  have  been  distinct  advances  made  in  the 
elucidation  of  the  chemical  nature  of  some  of  the  enzymes, 
but  there  is  no  definite  evidence  at  the  present  time  that 
any  has  been  obtained  in  a  pure  state,  that  is,  as  a  definite 
chemical  compound.  Notwithstanding  this  lack  of  knowl- 
edge, a  study  of  the  kinetics  of  a  number  of  enzyme  reactions 
has  led  to  the  view  that  primary  addition  products  are 
formed  between  the  enzyme  molecule  and  the  substrate 
(substance  acted  upon)  and  that  the  addition  products 
then  react  further  to  reform  the  enzymes  and  the  other 
products  of  the  reactions.  One  of  the  lines  of  evidence  for 
this  view  may  be  indicated  briefly.  With  a  small  amount 
of  enzyme  material,  increasing  the  amount  of  substrate  will 
at  first,  with  small  quantities  of  the  latter,  show  a  larger 
amount  of  decomposition  in  a  given  time  interval,  up  to  a 
certain  amount  of  substrate.  Increasing  the  concentra- 
tion of  substrate  beyond  this  will  result  in  the  same  amount 
of  action  as  with  the  smaller  amounts,  evidence  that  the 


68  CHEMICAL  REACTIONS. 

given  quantity  of  enzyme  can  take  care  of  only  a  certain 
quantity  of  substrate,  or  that  a  compound  of  the  two  is 
formed.  The  possible  question  of  adsorption  will  be  taken 
up  presently.  Another  way  of  stating  the  same  observa- 
tion is  that  with  small  amounts  of  enzyme,  the  amount  of 
substrate  transformed  in  a  given  time  interval  is  propor- 
tional to  the  length  of  the  time  interval.  Among  others, 
this  was  found  to  be  true  for  the  action  of  invertase  on  cane 
sugar  by  J.  M.  Nelson  and  W.  C.  Vosburgh  (Jour.  Am. 
Chem.  Soc.  39,  790  (1917)),  by  J.  Duclaux  [Chemie  Biolog- 
ique,  Paris,  1883;  and  Traite  de  Microbiologie,  Tome  II, 
Diastases,  Toxines,  et  Venims,  Paris,  1899],  by  A.  Brown 
(Trans.  London  Chem.  Soc.  81,  373  (1902)]  and  by  L. 
Michaelis  and  M.  L.  Menten  (Biochem.  Z.  49,  333  (1913)); 
of  amylase  on  starch  by  H.  T.  Brown  and  T.  A.  Glendinning 
[Trans.  London  Chem.  Soc.,  81,  388  (1902)];  of  the  action 
of  lactase,  maltase,  and  emulsin  by  E.  F.  Armstrong 
[Proc.  Roy.  Soc.  73,  500  (1904)];  of  lipase  on  glyceryl  tri- 
acetate by  K.  G.  Falk  and  K.  Sugiura  [Jour.  Amer.  Chem. 
Soc.  37,  227  (1915)]  and  of  urease  on  urea  by  D.  D.  van 
Slyke  and  G.  E.  Cullen  [Jour.  Biol.  Chem.  19,  141  (1914)]. 
The  well-known  lock  and  key  simile  of  Emil  Fischer  for 
such  reactions  indicates  also  a  belief  in  a  chemical  combina- 
tion as  the  first  step.  H.  D.  Dakin  [Jour,  of  Physiol.  30, 
253  (1904)  ]  found  evidence  for  the  existence  of  intermediate 
compounds  in  the  action  of  optically  active  liver  lipase 
material  on  a  racemic  mixture  of  esters  of  mandelic  acid, 
the  dextro-component  reacting  more  rapidly  than  the  laevo. 
"The  dextro-  and  Isevo-components  of  the  inactive  ester 
first  combine  with  the  enzyme,  but  the  latter  is  assumed 
to  be  an  optically  active  asymmetric  substance,  so  that  the 
rates  of  combination  of  the  enzyme  with  the  d-  and  1-esters 
are  different.  The  second  stage  in  the  reaction  consists 
in  the  hydrolysis  of  the  complex  molecule  (enzyme  +  ester). 
Since  the  complex  molecule  (enzyme  +  d-ester)  would  not 


CATALYSIS.  69 

be  the  optical  opposite  of  (enzyme  +  1-ester),  the  rate  of 
change  in  the  two  cases  would  again  be  different.  Judging 
by  analogy  with  other  reactions  one  might  anticipate  that 
the  complex  molecule  which  is  formed  with  the  greater 
velocity  would  be  more  rapidly  decomposed.  In  the  present 
case,  it  would  appear  that  the  dextro-component  of  the 
inactive  mandelic  ester  combines  more  readily  with  the 
enzyme  than  the  Isevo-component  does,  and  that  the  com- 
plex molecules  (d-ester  +  enzyme)  are  hydrolyzed  more 
rapidly  than  the  (1-ester  +  enzyme),  so  that  if  hydrolysis  be 
incomplete  dextro-acid  is  found  in  solution  and  the  residual 
ester  is  leevo-rotatory." 

The  views  so  far  presented  in  this  chapter  may  be  sum- 
marized as  being  based  upon  the  primary  formation  of 
addition  compounds  when  two  or  more  molecules  react,  these 
addition  compounds  then  breaking  down  to  form  new  mole- 
cules. In  catalytic  reactions,  the  first  stage  of  the  reaction 
is  the  same,  but  in  the  second  stage,  one  of  the  substances 
formed  in  the  breaking  down  of  the  intermediate  compound 
is  identical  in  composition  with  one  of  the  substances  which 
took  part  initially  in  the  reaction  in  the  formation  of  the 
addition  compound.  While  the  experimental  evidence  is 
favorable  to  this  view  of  catalytic  reactions  in  many  cases, 
it  may  be  objected  that  physical  influences  may  often 
modify  the  velocity  of  the  reaction  between  gases.  At 
present  there  is  no  experimental  evidence  of  any  kind 
available  to  prove  or  disprove  the  formation  of  definite 
chemical  compounds  in  such  cases,  but  on  the  other  hand, 
evidence  is  accumulating  that  adsorption  (or  perhaps  the 
solution  of  a  gas  or  a  liquid  in  a  solid)  is  the  important 
factor  here.  Just  how  far  phenomena  of  this  nature  may 
be  identical  with  the  formation  of  definite  chemical  com- 
pounds (possibly  so-called  "loose"  combinations)  on  a 
surface  is  not  at  present  certain,  but  until  direct  evidence 
is  obtained  that  such  reactions  must  be  included  in  a 


70  CHEMICAL  REACTIONS, 

scheme  different  from -the  one  outlined  here,  the  present 
classification  may  be  used  to  include  all  these  reactions, 
although  the  composition,  and  even  in  many  cases  the 
nature,  of  the  intermediate  compounds,  is  not  known. 

The  reactions  between  two  or  more  molecules  take  place 
with  the  formation  of  intermediate  compounds.  For  the 
sake  of  completeness,  it  will  be  necessary  to  refer  to  the 
reactions  in  which  one  substance  only  is  changing  or  re- 
acting. This  substance  may  be  a  simple  molecule  reacting, 
or  may  be  a  molecule  of  a  complex  intermediate  addition 
compound,  made  up  of  two  or  more  simpler  molecules. 
The  rate  of  such  reactions  appears  to  depend  entirely  upon 
the  nature  of  the  substance,  and  while  it  is  influenced  by 
the  temperature,  a  certain  fraction  of  the  amount  present 
is  transformed  in  each  unit  of  time,  the  monomolecular 
reaction  velocity  rate,  or  the  logarithmic  law,  being  fol- 
lowed. A  number  of  theories  have  been  suggested  to 
account  for  the  fact  that  only  such  a  part  reacts,  and  not 
the  whole  amount,  such  as  an  attempt  to  distinguish  be- 
tween active  and  inactive  molecules  of  a  substance,  of  which 
only  the  former  react,  while  a  constant  ratio  exists  between 
the  concentrations  of  the  two  kinds.  None  of  these  theories 
has  been  satisfactory,  and  for  the  present  at  least  it  is 
advisable  simply  to  state  the  fact  without  attempting  to 
explain  it. 

Some  theoretical  relations  with  regard  to  catalytic  re- 
actions will  now  be  taken  up.  A  simple  mechanical  analogy 
developed  by  Professor  J.  M.  Nelson  and  Dr.  J.  H.  North- 
rop, may  be  of  interest  here  in  considering  the  energy  or 
'affinity  relationships,  although  it  does  not  include  the 
view  of  addition  compound  formation. 

A  vessel  of  water,  A,  is  filled  to  the  level  C.  A  syphon,  D, 
filled  with  water  dips  into  this  water,  while  its  other, 
lower,  end  reaches  to  the  vessel  B  placed  lower  than  A,  so 
that  the  level  of  the  water  in  B  (E)  at  the  beginning  is 


CATALYSIS. 


71 


higher  than  the  bottom  of  vessel  A.  The  water  will  flow 
from  vessel  A  into  vessel  B  until  the  levels  in  the  two  are 
the  same.  In  this  analogy,  the  substances  initially  are 
represented  by  the  water  in  A, 
the  substances  after  the  reac- 
tion by  the  water  in  B,  the 
difference  in  the  content  of 
free  energy  is  shown  by  the  dif- 
ference in  level  in  the  two  ves- 
sels. The  change  of  the  substances  from  vessel  or  state 
A  to  vessel  or  state  B  of  lower  free  energy  content  takes 
place  through  the  syphon,  and  may  occur  in  a  number  of 
ways,  depending  upon  the  syphon.  Change  takes  place 
until  equilibrium  is  reached,  and  the  rate  of  change  depends 
upon  the  bore,  etc.,  of  the  syphon,  which  includes  therefore 
the  catalytic  influences.  The  raising  of  the  water  in  the 
left  arm  of  the  syphon  may  represent  the  work  necessary 
to  overcome  the  chemical  resistance,  this  work  being  re- 
gained in  the  other  arm  of  the  syphon.  The  catalytic 
properties  of  the  syphon  remain,  after  the  reaction,  the 
same  as  before,  and  the  reaction  would  proceed,  even  if 
the  bore  of  the  tube  were  infinitesimal,  but  at  an  infinitesi- 
mal rate. 

The  general  conditions  which  had  been  assumed  to  hold 
for  catalytic  reactions  and  which  were  used  to  determine 
whether  a  substance  acted  as  catalyst,  were  given  earlier  in 
this  chapter.  They  were  evolved  gradually  as  more  and 
more  reactions  of  this  nature  were  studied,  and  it  is  not 
surprising  therefore  that  this  superstructure  of  conditions 
became  top-heavy  and  that  some  of  the  conditions  assumed 
to  be  essential  in  a  catalytic  reaction,  at  times  were  found 
not  to  hold.  The  question  whether  the  equilibrium  point 
of  a  reaction  is  changed  by  a  catalyst  is  a  case  in  point. 
If  a  catalyst  only  changes  the  velocity  of  a  reaction,  and 
exerts  no  other  influence  whatsoever,  as  assumed  in  the 


72  CHEMICAL  REACTIONS. 

customary  statement  of  catalytic  changes,  then  the  catalyst 
cannot  change  the  equilibrium  of  the  reaction;  otherwise 
perpetual  motion  would  be  possible. 

From  time  to  time  statements  have  appeared  in  the 
literature  taking  exception  to  the  view  that  a  catalyst  does 
not  change  the  equilibrium,  without,  however,  going  to  the 
root  of  the  question  and  attempting  a  classification  and 
description  of  catalytic  actions  which  would  eliminate  such 
contradictions.  Thus,  G.  Bredig  (Ergebnisse  der  Physio- 
logic I,  139  (1902))  showed  that  a  change  in  the  vapor 
pressure  of  a  catalyst  necessitates  a  difference  in  the  work 
required  to  remove  the  catalyst  from  the  reaction  mixture. 
Only  as  long  as  this  work  is  the  same  under  the  same  condi- 
tions before  and  after  the  reaction,  does  the  equilibrium 
remain  unchanged.  If  the  catalyst  is  present  in  large 
excess  it  acts  as  solvent.  A  change  in  the  nature  of  the 
solvent  changes  the  equilibrium,  and  only  in  dilute  solution 
will  the  equilibrium  remain  the  same.  E.  Abel  [Z.  Elektro- 
chem.  13,  555  (1907)]  stated,  assuming  the  formation  of 
intermediate  products  with  the  catalyst,  that  if  the  catalyst 
is  in  a  different  chemical  or  physical  state  at  the  end  of  the 
reaction  from  what  it  was  at  the  beginning,  that  it  has 
given  up  or  received  energy,  and  that  a  change  in  the 
equilibrium  was  quite  conceivable.  W.  J.  Jones  and  A. 
Lapworth  [Trans.  London  Chem.  Soc.  99,  917  (1911)  found 
experimental  evidence  for  the  change  in  the  equilibrium 
between  ethyl  alcohol,  acetic  acid,  ethyl  acetate,  and  water, 
by  the  addition  of  the  catalyst  hydrogen  chloride.  M.  A. 
Rosanoff  (Jour.  Amer.  Chem.  Soc.  35,  173  (1913))  also 
speaks  of  the  possibility  of  a  catalyst  influencing  the  equi- 
librium, and  that  it  does  not  do  so  only  when  the  molecular 
state  of  the  reagents  is  not  affected  by  the  catalyst.  A 
number  of  other  chemists  may  be  quoted  in  the  same  sense. 
Recently,  W.  D.  Bancroft  (Jour.  Physical  Chemistry  21, 
573  (1917))  reviewed  certain  phases  of  catalytic  reactions 
and  took  up  some  of  the  questions  discussed  here. 


CATALYSIS.  73 

If  a  catalytic  reaction  is  defined  as  a  reaction  in  which 
one  of  the  products  is  identical  in  chemical  composition 
with  one  of  the  original  substances  involved  in  the  reaction, 
the  view  which  is  used  here,  then  it  may  be  possible  to 
arrive  at  definite  general  conclusions.  No  further  limita- 
tions are  introduced  in  the  definition.  In  the  general 
formulation  of  a  chemical  reaction  : 


in  which  0:10:2,  •  •  •  ai1,  a*1,  •••  represent  the  molecular  species 
in  the  solid  state  taking  part  in  the  reaction,  A\,  At,  •  •  •  AS, 
At'  ,  •  •  •  the  molecular  species  either  as  gas  or  in  solution, 
and  Fi,  F2,  •  •  •  n\,  n*,  •  •  •  V\,  F2',  •  •  •  n\,  rtz',  —  -  the  corre- 
sponding molecular  species  formed  in  the  reaction,  then  the 
definition  of  catalytic  action  advanced  requires  only  that 
one  of  the  molecular  species  a\,  0%,  •  •  •  A\,  A^,  •  •  •  is 
identical  in  composition  with  a\,  otz,  •  -  -  A\,  A%,  ••••.  The 
definition  does  not,  a  priori,  state  anything  concerning  the 
velocity  of  the  reaction.  Since  one  of  the  substances  ap- 
pears as  a  product  of  the  reaction,  obviously  it  may  go 
through  the  cycle  of  the  reaction  again  wjth  fresh  initial 
material.  This  substance  is  the  catalyst,  and  therefore 
a  small  amount  of  this  substance  may  react  with  a  large 
amount  of  the  other  substances.  This  phenomenon  has 
always  been  taken  to  be  one  of  the  most  characteristic 
properties  of  a  catalyst.  With  regard  to  the  possibility  of 
the  reaction  taking  place  in  the  absence  of  the  catalytic 
substance,  if  everyone  of  the  substances  at  the  beginning 
and  at  the  end  of  the  reaction  is  present  in  the  pure  state, 
then  the  equilibrium  constant  derived  from  the  law  of  mass 
action  would  be  independent  of  the  catalytic  substances,  the 
equilibrium  would  be  the  same  whether  the  catalyst  were 
present  or  not,  and  reaction  would  proceed  in  the  presence 


74  CHEMICAL  REACTIONS. 

or  absence  of  catalyst,  although  the  rates  in  the  different 
cases  may  well  be  different.  Furthermore,  it  is  impossible 
to  state  the  effect  of  the  catalyst;  it  might  increase  the  rate 
of  the  reaction,  it  might  decrease  it,  or  it  is  possible  that 
no  effect  at  all  would  be  noticeable  upon  the  rate  of  the 
reaction.  The  so-called  "negative  catalysis"  (cf.  Mellor, 
I.e.)  is  then  simply  a  special  case  of  catalysis  in  general,  the 
catalyst  here  retarding  the  reaction  instead  of  accelerating 
it. 

In  practical  work,  the  substances  taking  part  in  a  reaction 
are  hardly  ever  isolated  in  a  pure  state,  so  that  a  develop- 
ment of  the  ideal  case  just  presented  will  be  necessary. 
If,  in  the  general  formulation  of  a  chemical  reaction  given 
above,  the  concentrations  of  the  substances  A\,  A%,  •  -  -  A\  '  , 
AZ'J  -  -  -  in  the  free  state  before  and  after  the  reaction  are 
denoted  by  Ci,  C%,  •  •  •  d',  Cz',  •  •  •  and  their  concentrations 
at  equilibrium  by  c/,  c2',  •  •  •,  then  it  may  readily  be  shown 
that  the  change  in  the  free  energy  (^4)  of  the  reaction  is 
given  by  the  equation, 


(This  equation  ^  developed  with  the  aid  of  the  conception 
of  the  equilibrium  box  (van't  Hoff)  into  which  the  reacting 
substances  in  dilute  solution  or  the  gaseous  state  are  intro- 
duced through  suitable  semi-permeable  membranes,  in 
which  the  reaction  proceeds,  and  from  which  the  products 
are  removed  through  suitable  semi-permeable  membranes, 
all  isothermally  and  reversibly,  the  work  done  in  the 
different  steps  being  calculated  by  the  aid  of  the  gas  laws.) 
The  fraction  of  the  second  term  of  the  right  side  of  the 
equation  is  the  equilibrium  constant  K.  If  the  states  of 
the  substances  are  such  that  each  exists  independently 
before  and  after  the  reaction,  then,  even  if  CV'1  =  Cilnl 
as  necessary  for  a  catalytic  change,  the  work  done  will  be 


CATALYSIS.  75 

the  same  whether  the  catalyst  is  present  or  absent,  and  the 
equilibrium  will  be  unchanged.  If,  however,  work  is  done 
in  introducing  or  removing  the  catalyst,  some  sort  of  chem- 
ical compound  is  formed  between  two  or  more  of  the  molecu- 
lar species,  whether  this  be  termed  chemical  combination, 
solution,  adsorption,  physical  change,  etc.,  and  then  the 
terms  involving  the  concentrations  will  not  be  the  same  as 
before.  Thus  the  concentration  term  Cinl  may  denote  a 
complex  containing  the  catalyst,  while  in  the  denominator 
the  catalyst  may  be  represented  in  a  different  complex. 
It  may  be  said,  therefore,  that  in  the  chemical  changes  as 
ordinarily  observed,  if  a  catalyst  is  involved  in  the  reac- 
tion, that,  as  long  as  the  substances  are  not  present  in  the 
pure  state  or  possessing  the  same  properties  before  and 
after  the  reaction,  there  may  well  be  a  difference  in  the 
change  in  free  energy  of  the  reaction  in  the  absence  and 
presence  of  the  catalyst  and  that  the  equilibrium  will  be 
changed  correspondingly.  That  such  changes  have  not 
been  observed  more  frequently  than  has  actually  been  the 
case  is  doubtless  due  to  the  small  changes  in  the  equilibria 
which  have  resulted  by  the  addition  of  the  catalyst.  It 
must  also  be  remembered  that  the  law  of  mass  action  as  de- 
veloped in  the  thermodynamic  treatment  as  indicated, 
holds  only  for  dilute  solutions  and  for  gases  at  compara- 
tively low  pressures.  For  concentrated  solutions  and  gases 
at  high  pressures,  the  theoretical  considerations  cannot  as 
yet  be  applied  satisfactorily. 


CHAPTER  V. 

CHEMICAL   REACTIONS;     GENERAL  CONSIDERATIONS. 

IN  the  preceding  chapter  chemical  reactions  were  dis- 
cussed with  one  condition  fixed,  namely,  one  substance 
involved  in  the  reaction  having  the  same  chemical  composi- 
tion in  the  beginning  and  at  the  conclusion  of  the  reaction. 
Such  a  reaction  was  treated  as  a  catalytic  reaction  in  which 
the  substance  unchanged  in  composition  as  a  result  of  the 
reaction  acts  as  the  catalyst  and  causes  a  change  in  the 
velocity  of  the  reaction.  The  explanation  of  such  a  change 
in  velocity  is  to  be  found  in  the  addition  theory  of  chemical 
reactions  according  to  which  a  reaction  between  two  or 
more  molecules  takes  place  by  the  formation  of  a  more 
complex  intermediate  compound  which  then  breaks  down 
again  to  form  different  molecules.  The  presence  of  the 
catalytic  substance  may  accelerate  the  formation  (or  the 
decomposition)  of  the  complex  intermediate  compound  and 
in  this  way  increase  the  velocity  of  the  reaction,  being 
itself  reformed  as  one  of  the  products  of  the  decomposition 
of  the  intermediate  compound.  This  theory  of  addition 
compound  formation  will  now  be  applied  to  chemical  reac- 
tions in  general. 

The  formation  of  ammonium  chloride  was  discussed  to 
some  extent  in  the  preceding  pages.  The  reaction  is  a 
common  one,  relatively  simple,  and  as  will  be  seen,  repre- 
sentative of  a  large  group  of  chemical  transformations. 

Omitting  the  influence  of  catalytic  agents,  this  reaction 
may  be  considered  to  consist  in  the  formation  of  the  addition 
compound  ammonium  chloride  from  ammonia  and  hydrogen 
chloride.  The  simplest  and  most  common  way  of  express- 

76 


GENERAL  CONSIDERATIONS.  77 

ing  this  reaction  in  the  form  of  a  chemical  equation  is  the 
following : 

NH3  +  HC1  =  NH4C1  (1) 

The  reaction  indicated  by  this  equation  does  not  take 
place  under  ordinary  conditions  with  appreciable  velocity. 
When  ammonium  chloride  is  obtained  from  ammonia  and 
hydrogen  chloride,  water  or  moisture  is  present  as  a  rule, 
and  under  these  conditions,  the  reaction  takes  place  rapidly. 
The  equation  as  written  does  not,  therefore,  represent  the 
reaction  which  is  ordinarily  observed.  It  is  incomplete 
in  that  the  possible  action  o£the  catalyst,  water,  is  omitted. 
The  action  of  the  catalyst  is  of  the  highest  importance  here 
and  any  complete  explanation  of  the  reaction  must  neces- 
sarily include  it. 

In  the  last  chapter,  it  was  pointed  out  that  the  action 
of  the  catalyst  is  due  to  the  formation  of  addition  com- 
pounds between  the  catalyst  and  the  reacting  components 
and  that  these  addition  compounds  may  then  dissociate 
or  undergo  rearrangement,  yielding  the  final  reaction 
product  and  the  catalyst. 

In  the  particular  reaction  under  discussion,  the  formation 
of  ammonium  chloride,  water  is  known  to  form  addition 
compounds  with  both  the  reacting  components  and  with 
the  final  products.  Before  going  into  the  details  of  this 
reaction,  the  reaction  between  ammonia,  hydrogen  chloride, 
and  platinic  chloride  will  be  taken  up,  as  it  is  analogous  in 
certain  respects,  and  will  throw  some  light  on  the  nature 
of  the  intermediate  products  or  addition  compounds. 

The  behavior  of  ammonia  and  hydrogen  chloride  toward 
platinic  chloride  is  similar  to  their  behavior  toward  water; 
that  is,  addition  compounds  are  formed  in  both  groups. 
Because  of  the  different  characters  of  the  water  and  the 
platinic  chloride,  it  is  to  be  expected  that  the  dissociation 
or  decomposition  of  these  addition  compounds  (in  other 


78  CHEMICAL  REACTIONS. 

words,  their  stabilities,  as  measured  by  certain  equilibrium 
constants)  would  not  take  place  to  the  same  extent.  Bear- 
ing this  difference  in  mind,  the  formulations  may  now  be 
indicated. 

The  definite  compound  ammonium  chlor-platinate, 
(NH^PtCle,  is  made  up  of,  and  may  be  prepared  from, 
ammonia,  hydrogen  chloride,  and  platinic  chloride.  It  may 
dissociate  in  a  number  of  different  ways,  the  most  important 
of  which  are  indicated  by  the  following  equilibria : 

cl      =  2NH4C1  +  PtCl4  (a) 

=  2NH3  +  HJPtCle  (6) 


Cs, 


NH4       V\C1 

\C1 

Cl 


=  2HC1  +  (NH3)2PtCl4         (c) 
=  2NH3  +  2HC1  +  PtCl4     (d) 


(2) 


The  possible  intermediary  compounds  such  as  (NH4)PtCl5 
in  equilibrium  (a),  (NH3)2HPtCl5  in  equilibrium  (c),  etc., 
are  not  given,  as  they  add  nothing  to  the  principles  which 
these  equilibria  are  intended  to  illustrate.  Equilibrium  (d) 
represents  the  reaction  between  the  three  components  and 
the  "ternary"  intermediate  addition  compound.  The 
products  formed  according  to  the  equilibria  represented  by 
equations  (a),  (6),  and  (c),  may  all  be  present,  or  only 
some  of  them  may  be  formed.  The  extent  to  which  the 
different  products  are  found  depends  upon  the  equilibria 
of  the  various  reactions  under  the  conditions  of  temperature 
and  pressure  (or  concentration)  under  which  the  reaction  is 
being  studied.  The  equilibria  may,  of  course,  be  deter- 
mined experimentally,  and  the  values  of  the  equilibrium 
constants  give  a  measure  of  the  relative  chemical  affinities 
of  the  reactions.  If  the  conditions  are  such  that,  besides 
equilibrium  (d),  only  or  predominatingly  the  products 
shown  by  equilibrium  (a)  are  present,  then  the  platinic 
chloride  plays  the  part  of  a  catalyst  in  the  formation  of 
ammonium  chloride  from  ammonia  and  hydrogen  chloride. 
Again,  if,  besides  equilibrium  (d),  mainly  the  products 


GENERAL  CONSIDERATIONS.  79 

given  by  equilibrium  (6)  are  formed,  then  the  platinic 
chloride  is  not  the  catalyst,  but  on  the  other  hand,  ammonia 
would  be  acting  as  the  catalyst  in  the  formation  of  hydrogen 
chlorplatinate  from  platinic  chloride  and  hydrogen  chloride. 
Similarly,  if  equilibrium  (c)  were  the  predominating  re- 
action, hydrogen  chloride  would  act  as  the  catalyst  in  the 
formation  of  diammono  platinic  chloride  from  ammonia 
and  platinic  chloride.  The  concentrations  of  the  reacting 
substances,  according  to  the  law  of  mass  action,  would 
control  to  a  great  extent  in  any  given  case,  the  nature  of 
the  products  obtained.  If  the  reaction  is  not  allowed  to 
go  to  completion,  then  the  relative  reaction  velocities  of 
the  various  reactions  would  determine  the  composition  of 
the  mixture  at  any  instant. 

This  reaction  is  particularly  instructive,  since  the  com- 
position of  the  intermediate  addition  compound  is  perfectly 
definite.  With  equilibria  (a)  and  (d)  it  is  seen  that  the 
platinic  chloride  acts  as  the  catalyst  for  the  reaction  (either 
formation  or  decomposition,  depending  upon  the  concentra- 
tions of  the  reacting  substances)  between  ammonia,  hydro- 
gen chloride,  and  ammonium  chloride. 

The  influence  of  water  on  the  reaction  between  ammonia 
and  hydrogen  chloride  to  form  ammonium  chloride  may 
be  taken  up  in  the  same  way.  Although  very  little  is 
known  of  the  way  the  water  actually  catalyzes  the  formation 
of  ammonium  chloride,  the  reaction  considered  in  Chapter 
IV  in  the  formation  of  tetraethylammonium  iodide  from 
triethyl  amine  and  ethyl  iodide  in  the  presence  of  different 
solvents  indicated  the  method  of  action  of  the  catalyst. 
It  was  found  that  unsaturation  of  the  solvent  paralleled 
to  a  certain  extent  the  increase  in  the  velocity  of  the 
reaction.  Ability  to  form  addition  compounds,  inter- 
mediate or  otherwise,  seemed  to  be  the  controlling  factor. 
Unfortunately,  the  composition  of  the  intermediate  addition 
compound  is  not  so  definite  in  the  present  case.  In  order 


80  CHEMICAL  REACTIONS. 

to  show  the  reaction  in  as  simple  a  form  as  possible,  at  the 
same  time  coinciding  with  the  facts  as  far  as  known,  it  will 
be  assumed  that  the  "ternary"  addition  compound  contains 
one  molecule  of  hydrogen  chloride,  one  molecule  of  .am- 
monia, and  one  molecule  of  water.  The  formulation  of  the 
different  equilibria,  similar  £o  equations  (2),  will  then  be 
as  follows: 

=  (H2O.HG1)  +  NH3       (a) 

=  (H2O.NH3)  +  HC1       (b)  (3) 

=  H20  +  (NH3.HC1)       (c) 

=  H2O  +  NH3  +  HC1    (d) 

Starting  with  water,  ammonia,  and  hydrogen  chloride, 
[equilibrium  (d)],  it  is  found  experimentally  that  ordinarily 
the  products  indicated  by  equilibrium  (c)  are  obtained,  or 
vice  versa.  Water  acts  as  a  catalyst  for  the  reaction  between 
ammonia,  hydrogen  chloride,  and  ammonium  chloride,  just 
as  platinic  chloride  did  in  the  preceding  reactions.  A 
difference  between  the  two  sets  of  reactions,  (2)  and  (3), 
may  lie  in  the  fact  that  in  the  former,  (2),  the  value  of 
the  equilibrium  constants  may  be  such  as  to  show  the 
intermediate  "ternary"  compound,  ammonium  chlor- 
platinate,  to  be  more  stable  than  the  intermediate  "ternary" 
compound  in  the  latter,  (3).  Under  different  physical 
conditions,  such  as  increase  in  temperature,  etc.,  it  is 
possible  that  the  reaction  in  equations  (3)  would  proceed 
in  such  a  way  as  to  favor  the  formation  of  the  products  of 
(a)  or  of  (6).  The  changing  of  the  values  of  the  equilibrium 
constants  when  the  conditions  are  varied  may  well  cause 
the  reaction  to  assume  a  different  course.  All  the  possi- 
bilities, with  one  molecule  of  each  reactant,  are  given  in  the 
equations,  however,  and  the  deductions  are  similar  to  those 
from  equations  (2).  The  concentrations  of  the  reacting 
substances  here  also  play  a  predominating  role  in  deter- 
mining which  products  will  be  found  in  a  reaction  mixture. 


GENERAL  CONSIDERATIONS.  81 

The  actual  composition  of  the  ternary  compound  is  not 
known  definitely,  and  has,  therefore,  been  given  in  the 
simplest  form,  but  even  if  different  numbers  of  the  reacting 
molecules  were  contained  in  it,  the  same  principles  and 
relations  may  be  applied  although  the  equations  would  be 
much  more  complicated.  The  relative  velocities  of  the 
dissociation  of  the  intermediate  compound  would  determine 
which  products  are  observed  at  any  time,  if  the  complete 
reaction  has  not  been  allowed  to  come  to  equilibrium. 
It  is  perhaps  more  usual  to  speak  of  the  velocities  of  the 
various  reactions  than  of  the  values  of  their  equilibrium 
constants. 

To  return  to  the  formation  of  ammonium  chloride  in  the 
neutralization  of  ammonium  hydroxide  by  hydrochloric 
acid,  the  equation  for  the  change  may  be  written  as  follows 
in  which  the  presence  of  the  solvent,  water,  is  indicated: 

HC1.H2O  +  NH3.H2O  =  NH3.HC1  +  2H2O. 

It  is  evident  that  this  reaction  would  amount  to  a  change 
consisting  in  the  replacement  of  water  in  the  hydrate  of 
hydrogen  chloride  by  ammonia,  or  a  replacement  of  water  in 
ammonium  hydroxide  by  hydrogen  chloride.  This  reaction 
may  be  elaborated  further.  When  an  amine,  such  as 
ammonia,  is  dissolved  in  water,  it  combines,  in  part  at  any 
rate,  with  the  water  to  form  the  addition  compound  written 

*     +j        T?  + 

in  its  simplest  form  as  H3N.OH2  (or  graphically  H3N^OH2 
an  onium  addition  compound).  This  compound  may  tauto- 
merize  to  ammonium  hydroxide,  NH4OH,  the  base  from 
the  ionic  point  of  view,  which  may  be  written 


:N; 


[o'-Sj 


H  H 

in  two  zones  to  indicate  the  ionization,  and  which  shows  all 


82  CHEMICAL  REACTIONS. 

that  is  known  structurally  of  the  compound,  except  the 
formation  of  hydrates  (which  were  indicated  in  a  preceding 
chapter).  When  an  acid,  such  as  hydrochloric  acid  in 
water,  reacts  with  this  compound,  in  place  of  assuming  a 
direct  combination  between  hydrogen  and  hydroxyl  ions 
as  in  the  ionic  theory,  following  the  general  schemes  out- 
lined, an  addition  compound  is  considered  to  be  formed  first. 
The  complete  reactions  may  be  indicated  in  the  most  general 
wa  as  follows : 

(1) 


LH20-TLH2OJ         2H20 

In  equations  (1)  and  (2)  one  molecule  of  water  is  assumed 
to  take  part.  The  exact  number  is  unknown  and  is  im- 
material for  the  principle.  The  "binary"  compounds  are 
written  as  double  molecules.  Tautomerism  of  these  into 
the  ionizable  forms  may  take  place  and  probably  does 
so  and  reaction  (3)  to  form  the  "ternary"  compound  follows 
the  combination  of  the  two  "binary"  compounds.  This, 
then,  may  dissociate  according  to  equation  (4)  to  form 
ammonium  chloride  (or  more  probably  a  hydrate)  and 
water.  It  must  be  recalled  that  these  equations  are  all 
in  fact  really  equilibria,  and  that  the  reverse  reactions  may 
also  take  place.  Thus,  if  carbon  dioxide,  CO2,  were  used  in 
place  of  hydrogen  chloride,  very  little  of  the  products 
indicated  in  the  equation  corresponding  to  (4)  would  be 
present.  This  method  of  treating  the  subject  includes  also 
the  generalizations  derived  from  the  ionic  theory,  such  as, 
for  example,  the  heats  of  neutralization  of  highly  ionized 
acids  and  bases,  which  are  practically  identical  in  dilute 
solution.  This  is  brought  out  by  the  following  set  of 
equations : 


GENERAL  CONSIDERATIONS.  83 


(1) 
(2) 


[KOH]     [HCll  _  _  [KC1  ]  _  [K      1+    n 

[H20  J    •  [H20j       JJ*       '  |_3H2oJ  -  |_3H2oJ 


In  dilute  aqueous  solution,  in  reactions  (1)  and  (2)  a  greater 
number  of  molecules  of  water  undoubtedly  is  involved 
than  is  indicated.  The  "ternary"  addition  compound  of 
equation  (3)  is  made  up  as  indicated  but  may  rearrange  and 
then  ionize.  Comparing  the  final  product  of  (3)  with  the 
substances  present  in  great  excess  in  (1)  and  (2),  as  shown 
by  the  determinations  of  the  degrees  of  ionization,  it  is 
evident  that  the  net  change,  since  excess  of  water  is  present* 
is  the  combination  of  hydrated  H+  ion  and  OH  ion,  as 
postulated  by  the  ionic  theory.  The  mechanism  of  the 
change  shows  the  part  played  by  the  solvent  and  brings 
the  reaction  into  line  with  the  general  addition  reactions  of 
chemical  changes. 

To  come  back  to  the  main  subject,  it  becomes  evident 
that  many  of  the  neutralizing,  hydrolyzing,  and  double 
decomposition  reactions  are  in  fact  nothing  more  than 
replacement  reactions  whose  course  is  governed  by  the 
factors  indicated,  as  well  as  by  the  atomic  valences  and  co- 
ordination numbers  of  the  constituents  with  respect  to  the 
particular  substances  which  make  up  the  intermediate  ad- 
dition compound.  V 

Werner  (I.e.  pp.  232-7)  has  combined  all  these  reactions 
into  a  general  one,  which  may  perhaps  be  indicated  as 
follows  : 

XJA5MX]  +  H20  =  Xn[A5MH20]X  =  Xn[A5MOH]  +  HX. 

(1)  (2)  (3)  (4)  (5) 

One  molecule  of  water  may  react  with  compound  (1)  to 


84  CHEMICAL  REACTIONS. 

form  compound  (3).  This  primary  compound  may  then 
dissociate  to  yield  compounds  (4)  and  (5).  As  a  concrete 
example  chromium  chloride  may  be  taken  as  the  primary 
compound.  Here  M  is  Cr,  X  is  Cl,  and  n  is  2.  The 
equation  becomes: 

Cl2[(H2O)5CrCl]  +  H2O  =  Cl2[(H2O)5Cr(H2O)]Cl 

(1)  (2)  (3) 

=  Cl2[(H2O)5CrOH]  +  HC1. 

(4)  (5) 

Compounds  (1)  and  (2)  combine  to  form  (3);  this  is  hydra- 
tion.  Compounds  (1)  and  (2)  undergoing  double  decom- 
position form  (4)  and  (5);  this  is  hydrolysis.  The  forma- 
tion of  (1)  and  (2)  from  (4)  and  (5)  is  neutralization.  The 
formation  of  (1)  and  (2)  or  of  (4)  and  (5)  from  (3)  is  dissocia- 
tion. 

In  the  same  way  that  the  formation  of  ammonium 
chloride  from  ammonium  hydroxide  and  hydrochloric  acid 
could  be  considered  to  be  a  displacement  of  water  by 
hydrogen  chloride,  so  it  is  possible  to  consider  the  above 
set  of  reactions  in  the  case  of  the  chromium  chloride  to  be 
a  set  of  displacement  reactions.  Compound  (3)  may  be 
regarded  as  an  addition  compound  containing  both  hydro- 

[TTQTT  "I 
P  pi      is  equivalent 

[TTf^l      "1 
C  OH    '     Compound   (3)  therefore  can  dissociate  in 

either  direction,  giving  as  on£  of  the  products  hydrogen 
chloride  or  water.  The  reaction  in  which  compounds  (1) 
and  (2)  form  (4)  and  (5)  (hydrolysis),  is  therefore  a  dis- 
placement of  hydrogen  chloride  by  water.  Likewise,  the 
reaction  in  which  compounds  (4)  and  (5)  form  (1)  and  (2) 
(neutralization),  is  a  displacement  of  water  by  hydrogen 
chloride. 

The  reactions  considered  so  far  belong  to  the  general 


GENERAL  CONSIDERATIONS.  85 

group  which  may  be  classed  together  and  explained  most 
satisfactorily  as  addition  reactions,  in  which  intermediate 
addition  compounds  are  formed  which  are  in  equilibrium 
with  various  sets  of  products.  If  the  initial  and  final 
products  only  are  considered,  then  the  reactions  very  often 
appear  to  be  simple  replacement  reactions.  In  none  of 
these  reactions  has  the  charge  or  state  of  oxidation  of  any 
of  the  atoms  changed;  that  is  to  say,  no  oxidation  or  reduc- 
tion has  taken  place.  The  treatment  of  the  large  and  im- 
portant group  of  reactions  involving  oxidation  and  reduc- 
tion of  different  atoms  in  the  molecules  which  take  part  in 
chemical  reactions  will  be  taken  up  in  the  chapters  following 
these  on  addition  and  replacement  reactions. 

The  dissociation  of  an  intermediate  addition  compound 
into  several  sets  of  products  may  appear  at  times  to  be  a 
simple  reaction  which  leads  to  a  few  products.  To  indicate 
the  manifold  possibilities  and  complexities  which  might 
arise  from  the  dissociation  of  a  ternary  compound,  the 
following  scheme  may  be  given: 


r(A+m  #0*- 
C4&25)» 

L(A™* 


/ 

m 


IV 

)*  ~i 

etc. 


\  VI* 


\-(A+mBn)x        ~\ 

(A'&B&y 
L(A'^B^Z_J 


etc. 

0^-J 
VII 


In  this  scheme,  starting  with  x  molecules  of  A^B~,  y 
molecules  A'^B'nr,  and  z  molecules  A'^B'^T,  the  ternary 
addition  compound  I  is  formed.  The  molecules  A+B~ 


86  CHEMICAL   REACTIONS. 

are  assumed  not  to  exchange  positive  or  negative  con- 
stituents, but  to  dissociate  as  the  integral  molecules  which 
make  up  the  ternary  compound.  Under  these  simplified 
conditions,  it  is  seen  how  the  dissociation  may  take  place, 
and  the  number  of  possible  equilibria  involved  in  a  reaction 
of  this  type.  If  the  various  positive  or  negative  constitu- 
ents may  in  addition  replace  or  displace  each  other,  the 
number  of  equilibria  is  correspondingly  increased.  This 
scheme  shows  why  the  number  of  products  in  many  organic 
reactions  is  so  large.  In  inorganic  reactions,  in  which  the 
number  of  reacting  components  is  smaller  as  a  rule,  the 
possibilities  as  to  the  number  of  products  formed  are  smaller, 
but  it  must  be  emphasized  again  that  the  general  principles 
of  the  mechanism  of  chemical  reactions  apply  throughout, 
whether  these  be  grouped  for  convenience  of  treatment  or 
for  any  other  reason  as  inorganic  and  organic  reactions. 

Since  the  ionic  theory  has  been  so  successful  in  correlating 
a  number  of  previously  separated  phenomena,  including 
the  possible  explanation  of  certain  chemical  reactions, 
especially  those  taking  place  in  aqueous  solution,  it  is  of 
importance  to  try  to  find  to  what  degree  the  explanations 
based  upon  it  are  accepted  at  present,  and  how  the  objec- 
tions may  be  met  most  satisfactorily  by  the  newer  develop- 
ments. In  this  book  the  facts  of  the  ionic  theory  are 
accepted,  but  some  of  the  shortcomings  of  the  theory,  such 
as  the  part  played  by  the  solvent,  have  already  been 
pointed  out.  It  was  shown  how  the  mechanism  of  a 
number  of  chemical  reactions  might  well  be  explained  more 
satisfactorily  on  the  basis  of  the  addition  theory.  The 
statement  made  by  a  few  zealous  supporters  of  the  ionic 
theory  that  only  ions  take  part  in  chemical  reactions  may 
be  dismissed  without  much  consideration.  This  has  never 
been  the  view  of  the  greater  number  of  workers  who  have 
always  recognized  the  occurrence  of  reactions  especially 
with  organic  compounds  in  which  no  ionization  (as  the 


GENERAL  CONSIDERATIONS.  87 

ionic  theory  understands  ionization)  was  present.  This 
fact,  however,  at  once  separates  reactions  into  two  groups, 
ionic  and  non-ionic.  Just  as  with  the  suggestion  of  two 
kinds  of  valence,  polar  and  non-polar,  as  shown  in  an  earlier 
chapter,  this  divides  chemistry  into  two  branches,  with 
separate  sets  of  explanations  for  each.  The  addition  theory 
includes  all  reactions  and  formulations,  and  offers  one  set 
of  explanations  for  the  two  sets,  at  the  same  time  including 
the  relations  developed  by  the  ionic  theory  as  part  of  the 
general  development.  Reference  may  be  made  to  a  paper 
by  J.  W.  Walker  (Trans.  Chem.  Soc.  85,  1082  (1904))  in 
this  connection.  To  indicate  the  application  of  the  addi- 
tion theory  to  inorganic  reactions,  a  typical  example  of  a 
reaction,  explained  heretofore  on  the  basis  of  the  ionic 
theory,  will  be  described. 

The  reactions  between  some  metallic  salts,  ammonium 
salts,  and  ammonia  will  be  taken  up  briefly.  Many  of  the 
bivalent  metals  such  as  nickel,  magnesium,  etc.,  form 
hydroxides  insoluble  in  water  but  soluble  in  solutions  of 
ammonium  salts.  The  generally  accepted  explanation  for 
the  solubility  in  solutions  of  ammonium  salts  or  for  the 
non-precipitation  by  ammonia,  if  ammonium  salts  are 
present,  is  that  the  ammonium  ion  of  the  ammonium  salts 
drives  back  or  represses  the  electrolytic  dissociation  of  the 
ammonium  hydroxide  so  that  the  hydroxide  ion  is  not 
present  in  sufficient  concentration  to  exceed  with  the  metal 
ion  the  solubility  product  of  the  metal  hydroxide.  The 
new  explanation  depends  upon  hydrolytic  reactions  and 
equilibria  as  outlined. 

A    bivalent    metal    halide,    MX2,    will    be    chosen   as 

H2 

^/O X 

an  example.     In  water  the  compound  Mx^  will  be 

^O — X 
H2 

present  and  negative  X  combined  with  O  carrying  a  pre- 

7 


88  CHEMICAL   REACTIONS. 

dominatingly  negative  charge  will  ionize  into  [M(OH2)2]~H~ 
and  2X.  It  is  probable  that  a  substance  of  this  sort 
will  take  up  more  (generally  four)  molecules  of  water 
in  onium  combination  with  the  metal  element.  These 
additional  molecules  of  water  are  not  directly  involved 
in  the  theoretical  views  to  be  developed  and  will  therefore 
be  omitted.  The  substance  M(OH2)2X2  may  undergo 
hydrolytic  dissociation  as  shown  in  equilibrium  (6)  of  the 
reaction. 


2)8+  2x    (a) 

g  —  X  =   M(OH)2     +     2HX   (b) 

^2 

The  reaction  which  will  be  observed  depends  upon  the 
equilibria  (affinity  relationships)  of  (a)  and  (b)  in  the  given 
equations,  and  upon  the  addition  or  removal  of  any  of  the 
products.  For  instance,  equilibrium  (b)  will  proceed  to 
the  right  if  a  base  is  added.  The  addition  of  the  base 
removes  HX  and  causes  more  M(OH2)2X2  to  undergo 
hydrolysis  until  ultimately  only  M(OH)2  will  be  present. 
This  reaction  will  take  place  especially  if  M(OH)2  is  in- 
soluble, but  it  is  important  to  note  from  these  equations 
that  it  is  due  to  the  removal  of  HX  by  the  base  rather  than 
direct  metathesis.  The  simplest  way  of  looking  at  the 
change,  if  only  the  initial  and  final  substances  and  their 
formulas  are  used,  is  MX2  +  2M'OH  =  M(OH)2  +  2M'X; 
but  this,  for  one  thing,  leaves  out  of  account  the  action  of  the 
solvent.  Written  in  the  ionic  form  M  +  2OH  =  M(OH)2, 
while  apparently  going  back  to  more  fundamental  relation- 
ships, does  not  show  what  direct  part,  if  any,  the  solvent 
plays.  By  means  of  the  equilibrium  reactions  as  formu- 
lated, the  part  the  solvent  plays  is  made  evident.  Further- 
more, the  reaction  is  brought  into  line  with  a  great  number 
of  others  included  among  hydrolytic  reactions. 


GENERAL  CONSIDERATIONS.  89 

Ammonia  is  analogous  to  water  in  its  reactions.  As 
stated  before,  onium  compounds  are  formed  to  a  greater  or 
more  readily  observable  extent  with  it  than  with  water.  If 
ammonia  is  added  to  a  solution  of  MX2,  it  is  evident  that 
a  compound  (H3N^)4M(-*NH3-»)2X2,  or  (omitting  the 
four  ammonias  in  onium  combination  with  M),  M(NH3)2X2, 
may  be  formed.  The  relative  amounts  of  M(OH2)2X2  and 
of  M(NH3)2X2  which  will  be  formed,  or  the  distribution  of 
MX2  between  water  and  ammonia,  will  depend  upon  the 
relative  stabilities  of  these  compounds  under  the  given 
conditions.  The  substance  M(NH3)2X2  undergoes  electro- 
lytic dissociation  as  follows  (omitting  possible  intermediate 

ions) : 

H3 

M<N    -  X  =  [M(NH3)2]+++2X. 
H3 

Ammonolytic  dissociation  to  form  M(NH2)2  and  HX, 
analogous  to  the  hydrolysis  of  the  hydrated  salt,  does  not 
seem  to  occur  with  these  compounds  under  these  condi- 
tions. (Possibly  the  mercury  ammonia  compounds  dis- 
sociate in  this  way  under  suitable  conditions.)  The  addi- 
tion of  a  base  has,  therefore,  no  direct  action  on  a  substance 
of  this  formula  in  the  way  of  influencing  the  equilibrium. 
Beyond  the  possibility  of  a  direct  metathetical  reaction,  the 
base  plays  no  part,  as  it  does  in  the  hydrated  salt,  even  if 
the  hydroxide  is  not  soluble.  To  sum  up,  the  possible 
reaction  between  a  base  and  a  substance  MX2  in  water  in 
the  presence  of  ammonium  salts  or  ammonia,  will  depend 
upon  the  relative  amounts  of  hydrated  and  ammoniated  salt 
present;  if  an  appreciable  amount  of  the  former  is  present, 
M(OH)2  may  be  precipitated;  if  the  salt  is  entirely  present 
as  the  latter,  no  M(OH)2  will  be  precipitated. 

In  the  past  years,  F.  Ephraim  published  some  very 
careful  studies  on  the  stability  of  the  metal  ammoniates. 
He  determined  the  temperatures  at  which  the  hexa- 


90  CHEMICAL  REACTIONS. 

ammonia  (and  substituted  ammonia)  derivatives  of  a 
number  of  salts  of  the  bivalent  metals  (including  Be,  Ni,  Co, 
Fe,  Cu,  Mn,  Zn,  Cd,  Mg)  showed  definite  vapor  pressures. 
The  resuUs  give  a  measure  of  the  relative  stabilities  of 
these  compounds,  and  consequently  also  for  solutions  of 
them.  This  gives  no  direct  evidence  as  to  the  distribution 
of  any  given  salt  between  water  and  ammonia  with  both 
present  in  solution,  but  does  give  a  relative  measure  of  the 
amounts  of  the  ammoniates  formed  by  a  number  of  different 
salts.  For  instance,  the  salt  NiCl2.6NH3  shows  a  vapor 
pressure  of  500  mm.  at  130°,  while  the  salt  MgCl2.6NH3 
shows  the  same  vapor  pressure  at  24.5°.  This  means  that 
a  very  much  smaller  concentration  of  ammonia  would  be 
needed  in  solution  to  form  the  hexa-ammoniate  with  a 
nickel  salt  than  would  be  necessary  for  a  magnesium  salt. 
Consequently,  as  a  result  of  the  distribution  of  the  salt 
between  the  ammonia  and  the  water,  the  concentration  of 
ammonium  salt  needed  to  prevent  the  precipitation  of  the 
metal  hydroxide  if  a  base  is  added  would  be  much  less  for 
the  nickel  salt  than  for  the  magnesium.  The  salts  studied 
by  Ephraim  may  be  arranged  in  a  series  showing  the  relative 
amounts  of  ammonium  salts  needed  to  prevent  precipitation 
if  a  base  is  added. 

The  views  of  Werner  that  compounds  of  the  first  order 
are  not  electrolytes  but  must  go  over  into  compounds  of 
higher  orders  before  becoming  electrolytes  bear  upon  this 
question.  They  have  already  been  given  and  need  only 
be  mentioned  here. 

Reference  may  also  be  made  (o  two  experimental  investi- 
gations bearing  on  this  question:  Isbekow  [Z.  anorg. 
Chem.  84,  24  (1914)]  found  that  by  dissolving  the  sub- 
stances mercuric  bromide,  antimony  bromide,  bismuth 
bromide,  carbon  tetrabromide,  etc.,  in  molten  aluminium 
bromide  as  solvent,  solutions  were  obtained  which  gave 
abnormally  high  molecular  weights  for  the  solute  and  which 


GENERAL  CONSIDERATIONS.  91 

conducted  the  electric  current.  Isbekow  attributed  this 
high  molecular  weight  to  association  of  the  solute  or  to  a 
combination  of  the  solute  with  solvent,  and  thought  that 
these  complex  substances  were  responsible  for  the  ioniza- 
tion  and  conduction  of  the  current.  Isbekow's  discussion 
of  his  results  is  of  interest  and  may  be  given  as  follows : 

"The  associated  condition  of  the  electrolytes  dissolved  in 
AlBra  is  not  a  general  characteristic  of  molten  salts  and  their 
mixtures.  Although  Lorenz  [Z.  phys.  Chem.  70,  230 
(1910)]  has  shown  that  a  marked  association  occurs  in  the 
case  of  molten  salts,  still  as  has  been  pointed  out  by  the 
investigations  of  Sackur  [Z.  phys.  Chem.  78,  550  (1912)], 
the  substances  dissolved  in  molten  salts,  in  many  cases, 
break  down  into  simple  ions,  and  in  dilute  solutions  of 
salts  of  the  type  MX2  as  solvent,  the  dissociation  is  com- 
plete. A  relationship  of  this  kind  was  also  observed  by 
Tolloczko  [Z.  phys.  Chem.  30,  705  (1899)]  and  by  Klemen- 
siewicz  [Bull,  de  1'academie  des  Sc.  de  Cracowie  (1908)  p. 
485)],  in  solutions  of  the  alkali  salts  in  SbCla.  On  the 
other  hand,  electrolytes  dissolved  in  molten  HgCk  show 
association  as  in  AlBr3.  The  individual  influence  of  each 
solvent  is  also  evident  in  the  case  of  molten  salts,  one 
solvent  possessing  the  ability  to  ionize  principally  simple 
molecules  another  principally  complex  molecules.  There- 
fore, each  electrolyte  solution  is  undoubtedly  the  result 
of  a  particular  interaction  between  the  two  components, 
since  the  same  substance,  in  one  solvent  conducts  and  in  the 
other  does  not.  This  interaction  manifests  itself  in  many 
cases  in  the  participation  of  the  solvent  in  the  formation  of 
the  complex  molecule  or  complex  ion.  It  is  not  improbable, 
that  in  the  above  thermal  experiments,  such  a  participation 
of  the  solvent  occurs."  If  Isbekow's  interpretation  is 
correct,  the  solvent  and  solute  interact  to  form  the  electro- 
lyte, similar  to  the  formation  of  the  ionogen  ammonium 
chlorplatinate,  (NH4)2PtCl6,  from  platinic  chloride  and 


92  CHEMICAL  REACTIONS. 

ammonium  chloride.  The  constitution  of  these  ionogens 
would  be  of  the  form  (AlBr3)n(MX)m. 

It  was  shown  by  Plotnikoff  (J.  Russ.  Phys.  Chem.  Soc. 
(3)  466  (1902))  and  later  confirmed  and  studied  more 
thoroughly  by  H.  E.  Patten  (J.  Physical  Chem.  8,  564 
(1904)),  that  aluminium  bromide  dissolved  in  ethyl  bromide 
gives  a  solution  which  has  a  relatively  low  electrical  re- 
sistance, and  from  which  aluminium  may  be  deposited 
electrolytically  just  as  in  the  case  of  a  solution  of  an 
aluminium  salt  in  water.  Another  interesting  fact  about 
these  results  is  that  ethyl  bromide  has  a  very  low  dielectric 
constant  (8.9)  and  still  serves  as  an  ionizing  medium  for 
the  aluminium  bromide.  This  solution  is  analogous  to  the 
solutions  described  by  Isbekow. 

It  must  be  borne  in  mind,  however,  in  interpreting  these 
last  results,  that  the  separation  of  a  metal  or  other  sub- 
stance at  an  electrode  bears  no  relation  necessarily  to  the 
nature  of  the  ions  which  may  be  present  in  solution.  For 
example,  copper  may  be  deposited  on  the  cathode  from  a 
solution  of  potassium  copper  cyanide,  in  which  all  except 
perhaps  a  minute  part  of  the  copper  is  contained  in  the 
anion. 

Other  evidence  with  regard  to  the  combination  of  solvent 
and  solute  might  be  quoted,  but  the  general  trend  of  the 
views  is  apparent.  As  for  the  reasons  for  a  substance 
being  able  to  dissolve  another  substance  and  of  inducing 
ionization,  a  number  of  suggestions  have  been  put  forward, 
especially  for  the  latter  phenomenon.  Thus,  W.  Nernst 
and  J.  J.  Thomson  have  considered  it  to  be  due  to  the 
dielectric  constant  of  the  solvent,  J.  Bruhl  to  the  (chem- 
ically) unsaturated  nature  of  the  solvent,  etc.  While  all 
of  these  views  possess  a  certain  amount  of  truth  for  various 
solvents,  there  is  at  present  no  general  explanation  which 
covers  all  the  facts.  Possibly  the  development  of  the  views 
.put  forward  here  involving  addition  compounds,  tautomeric 


GENERAL  CONSIDERATIONS.  93 

rearrangements,  and  equilibria  with  different  sets  of 
products  may  permit  of  a  more  general  theory,  but  at 
present,  the  quantitative  data  with  regard  to  these  addition 
products  are  too  meagre  to  permit  of  more  than  a  suggestion 
of  this  as  a  general  explanation. 


CHAPTER  VI. 

SOME  CHEMICAL  REACTIONS. 

THE  principles  developed  in  the  preceding  chapters  will 
now  be  applied  to  chemical  reactions,  the  substances  re- 
acting, and  the  probable  mechanism  or  course  of  the 
reactions,  involving  at  the  same  time  a  classification  of  these 
changes.  The  difficulty  which  arises  in  these  applications 
is  due  to  the  wealth  of  material  available,  especially  in  the 
changes  included  in  organic  chemistry.  There  is  a  strong 
temptation  to  include  all  reactions  which  have  been  de- 
scribed and  if  this  were  done  this  book  would  resolve  itself 
into  a  compendium  of  reactions,  interesting  perhaps  in 
itself,  but  lacking  a  point  of  view  by  which  it  was  intended 
to  systematize  such  reactions  as  far  as  possible.  The 
applications  in  this  and  the  following  chapter  in  the  first 
place  will  include  only  reactions  in  which  none  of  the  atoms 
in  any  of  the  reacting  molecules  shall  have  changed  its 
valence  or  become  oxidized  or  reduced.  Reactions  in- 
volving such  changes  will  be  taken  up  in  later  chapters. 
In  this  and  the  following  chapter  a  number  of  reactions 
will  be  discussed  from  the  point  of  view  of  the  mechanism 
or  course  of  the  reactions.  Since  so  much  material  is 
available  in  the  field  of  organic  chemistry,  practically  all 
these  reactions  involve  changes  in  organic  compounds,  and 
it  will  be  shown  how  a  number  of  reactions  which  heretofore 
have  been  considered  to  be  different  may  be  included  in 
one  general  point  of  view.  In  the  succeeding  chapter,  the 
changes  which  one  group  of  substances,  the  olefins,  undergo 
will  be  discussed  and  compared  with  the  changes  taking 
place  in  various  organic  and  inorganic  reactions.  In  this 
way,  by  considering  first  the  changes  involved  in  a  series 

94 


SOME  CHEMICAL  REACTIONS.  95 

of  reactions,  and  then  the  changes  undergone  by  a  group 
of  substances  it  is  hoped  to  bring  out  the  general  principles 
involved  in  the  mechanism  of  chemical  reactions,  without 
unduly  elaborating  the  details  of  innumerable  reactions. 

The  Friedel-Crafts  reaction  is  one  of  the  most  useful 
reactions  in  preparative  organic  chemistry.  In  most  text 
books,  the  reaction  is  discussed  in  connection  with  the 
synthesis  of  alkyl  and  acyl  derivatives  of  the  aromatic 
hydrocarbons.  It  will  be  seen  in  the  following  pages  how- 
ever that  this  is  a  somewhat  misleading  and  incomplete 
view,  since  there  are  a  great  number  of  reactions  involving 
the  use  of  aluminium  chloride  which  are  not  included  in  the 
above  classification.  With  regard  to  the  changes  occurring 
in  the  Friedel-Crafts  reaction,  the  aluminium  chloride  does 
not  appear  in  the  final  product.  The  reaction  as  carried 
out  in  the  laboratory  is  very  often  done  in  steps,  first 
bringing  together  the  components,  perhaps  in  the  presence 
of  a  diluent  such  as  carbon  disulfide;  and  second,  decom- 
posing the  reaction  mixture  with  water  with  the  formation 
of  the  desired  substance  or  substances  and  removal  of  the 
aluminium  as  chloride  or  hydroxide,  etc.  Since  aluminium 
chloride  may  be  present  after  the  reaction  has  proceeded 
to  a  certain  point,  it  may  be  assumed  as  a  first  consideration 
to  play  the  part  of  a  catalyst.  A  brief  review  of  the 
theoretical  explanations  proposed  at  different  times  to 
account  for  the  mechanism  of  the  reaction  will  first  be  given. 

C.  Friedel  and  J.  M.  Crafts  described  the  reaction  in 
1877  [J.  pr.  Chem.  16,  233.]  Two  typical  reactions  given 
by  them  were  (1)  the  formation  of  amylbenzene  from  amyl 
chloride  and  benzene  and  (2)  the  formation  of  benzophenone 
from  benzoyl  chloride  and  benzene,  both  in  the  presence  of 
aluminium  chloride  and  giving  hydrogen  chloride  as  by- 
product. They  suggested  the  following  equations  as  an 
explanation  of  the  first  reaction : 


96  CHEMICAL  REACTIONS. 

C6H6  +  A12C16  =  HC1  +  A12C15C6H5, 

(hypothetical  compound) 

A12C16C6H5  +  C6HUC1  =  A12C16  +  CeHBCCfiHu). 

They  assumed  the  formation  of  the  hypothetical  inter- 
mediate compound  A12C15C6H5  in  this  reaction  and  of  similar 
compounds  in  other  reactions.  This  theory  has  never 
been  demonstrated  experimentally  to  be  true  and  has, 
therefore,  been  superseded  by  other  theories. 

The  dominating  idea  in  Friedel  and  Crafts'  original  theory 
and  in  most  of  the  theories  attempting  to  explain  the  re- 
action is  the  formation  of  more  complex  compounds  first, 
followed  by  their  decomposition  or  further  reaction. 

G.  Perrier  [C.r.  116,  1300  (1893);  Ber.  33,  815  (1900)] 
found  that  in  the  Friedel-Crafts  reaction  for  the  formation 
of  ketones  from  hydrocarbons  and  acyl  halides,  the  acyl 
halides  and  also  the  ketones  formed  in  the  reaction  formed 
addition  compounds  with  the  aluminium  halides  which  he 
was  able  to  isolate: 

2RCOC1  +  A12C16  =  (RCOC1)2A12C16, 
(RCOC1)2A12C16  +  CwHn  =  2HC1  +  (RCOCWHB_1)2A12C16. 

The  decomposition  of  the  addition  compound  (which  formed 
a  crystalline  compound)  with  cold  water  yielded  the  ketone. 
The  formation  of  these  compounds  has  since  been  confirmed 
by  several  other  investigators  and  has  enabled  them  to  study 
the  kinetics  of  this  reaction  in  the  case  of  acyl  halides. 

G.  Gustavson  proposed  the  theory  that  the  aluminium 
chloride  formed  intermediate  addition  compounds  of  the 
type  A1X3C6H6  and  A1X3.3C6H6  [J.  pr.  Chem.  68,  209 
(1903)],  and  that  in  the  course  of  the  reaction  these  addi- 
tion compounds  reacted  with  the  alkyl  halides  to  form  the 
reaction  products.  For  the  preparation  of  these  addition 
compounds,  he  passed  dry  hydrogen  chloride  into  a  mixture 
of  aluminium  chloride  and  the  hydrocarbon  [Ber.  11,  2151 


SOME  CHEMICAL  REACTIONS.  97 

(1878)].  They  could  not  be  obtained  in  crystalline  form 
however  and  recently  some  doubt  has  been  cast  on  their 
existence.  Gustavson  finally  succeeded  in  obtaining  a 
crystalline  compound  which  had  the  composition  2  A1C13.- 
2  C6H3[CH(CH3)2]3.HC1  [C.r.  140,  940  (1905);  J.  pr.  Chem. 
72,  57  (1905)],  but  this  does  not  conform  to  the  above  type 
and  is  really  a  ternary  compound. 

B.  N.  Menschutkin  [J.  Russ.  Phys.  Chem.  Soc.  41,  1089 
(1909);  Chem.  Zentralb.  1910,  1,  167]  showed  that  the 
freezing  point  curves  of  mixtures  of  aluminium  halides  and 
benzene  or  toluene  gave  no  indication  of  the  formation  of 
any  such  addition  compounds  as  claimed  by  Gustavson. 
Many  chemists  are  inclined  to  accept  the  results  of  Men- 
schutkin as  conclusive  evidence  that  aluminium  halides  and 
benzene  or  toluene  do  not  form  any  addition  compounds. 
On  the  other  hand,  all  that  the  freezing  point  curve  shows 
under  these  conditions  is  that,  even  if  formed,  not  enough 
of  the  addition  compound  was  present  to  saturate  the 
solution.  Furthermore,  Menschutkin  found  that  in  the 
case  of  other  metal  halides  such  as  antimony  chloride, 
addition  compounds  such  as  SbCl3.C6H6  can  be  obtained 
[C.  A.  (1911)  1434)].  It  must  also  be  borne  in  mind  in 
comparing  these  results  with  the  results  of  Gustavson,  that 
the  latter  in  his  experiments  had  hydrogen  chloride  present 
as  well.  •*.-.. 

J.  Boeseken  and  co-workers  [Rec.  trav.  chim.  32,  184 
(1913);  33,317',  34,78;  35,109;  Verslag  Akad.  Wenschap- 
pen  21,  979]  studied  the  Friedel-Crafts  reaction  in  connec- 
tion with  sulfonyl  chlorides  such  as  p-brombenzene- 
sulphonechloride,  etc.  These  combined  with  the  aluminium 
chloride.  The  resulting  compounds  then  reacted  with  the 
aromatic  hydrocarbon.  The  sulfone  formed  in  the  reaction 
combined  with  the  aluminium  chloride,  and  if  formed  in 
considerable  amount  decreased  the  velocity  of  the  reaction 
by  decreasing  the  concentration  of  the  double  salt  of  the 
sulfone  chloride  and  aluminium  chloride. 


98  CHEMICAL  REACTIONS. 

There  is  considerable  experimental  evidence  at  hand, 
therefore,  for  the  formation  of  double  salts  or  binary  com- 
pounds from  acid  chlorides  and  alumin'um  halides.  In 
addition  to  the  examples  given,  E.  P.  Kohler  [Am.  Chem.  J. 
24,  390  (1900)]  iso'ated  the  compounds  A^Br3  C6H5SO2C1, 
AlBr3.C6H5COCl,  AlBr3.POCl3,  AlBr3.C6H5COCH3,  and 
AlBr3.C6H5NO2,  and  Abegg  [Handbuch  der  anorganischen 
Chemie,  vol.  3,  part  1,  p.  74  (1906)]  mentions  the  com- 
pounds A1C13.SC14;  A1C13.2PC13;  A1C13.2KC1;  A1C13.4KC1; 
A1C13.4NH4C1;  etc.  The  ability  of  aluminium  halides  to 
combine  to  form  complex  compounds  is  also  shown  in  the 
following  substances  which  have  been  described : 

AlCl3.HgCl.C6H6  W.  Gulewitsch  [Ber.  37,  1560  (1904)]; 
A1C13.(C2H5)2O;  A1C13.C6H5OCH3;  A1C13.C6H5CO2C2H5; 
C2H5Br.H2S.AlBr3  [V.  A.  Plotnikoff,  J.  Chem.  Soc.  Abstr. 
(1913),  1,  1295],  etc. 

The  evidence  for  the  formation  of  binary  compounds  with 
aluminium  halides  and  acyl  halides,  inorganic  halides  and 
a  number  of  organic  substances  containing  oxygen  but  no 
halogen  is  satisfactory.  On  the  other  hand,  the  evidence 
at  hand  concerning  addition  compounds  from  -  aromatic 
hydrocarbons  and  alkyl  halides  has  failed  to  show  their 
presence.  For  example,  A.  Wroczynski  and  P.  A.  Guye 
[J.  chim.  Phys.  8,  189  (1910)]  found  that  the  freezing  point 
curve  of  a  mixture  of  benzene  a-nd  chloroform  gave  only  one 
eutectic,  and  Schmidlin  and  Lang  observed  the  same  with 
the  benzene-bromoform  system. 

B.  N.  Menschutkin  [Chem.  Zentralbl.  (1910),  I,  167]  and 
also  J.  Boeseken  [Chem.  Zentralbl.  (1911),  I,  466]  suggested 
that  in  the  Friedel-Crafts  reaction  the  three  reacting  com- 
ponents combined  to  form  a  ternary  compound  which  then 
reacted  further.  This  view  was  adopted  and  elaborated  by 
J.  Schmidlin  and  R.  Lang  [Ber.  45,  899  (1912)].  They 
considered  the  evidence  for  the  existence  of  binary  com- 
pounds described  above,  and  concluded  that  the  only  satis- 


SOME   CHEMICAL  REACTIONS.  99 

factory  explanation  lay  in  the  formation  of  ternary  com- 
pounds. As  positive  evidence  they  cited  the  solubility  of 
aluminium  chloride  in  cold  mixtures  of  benzene  or  toluene 
and  alkyl  halides  forming  filterable  solutions  which  evolve 
hydrogen  chloride  upon  being  warmed,  and  also  the  increase 
in  conductivity  observed  when  benzene  or  toluene  was 
added  to  a  solution  of  aluminium  chloride  in  ethyl  bromide 
[J.  W.  Walker,.Trans.  Chem.  Soc.  84,  1082  (1904)]. 

There  have  been  several  other  theories  proposed  for  the 
mechanism  of  this  reaction  where  no  consideration  was 
given  to  the  existence  of  addition  compounds.  Among 
these  may  be  mentioned  the  theory  of  J.  U.  Nef  [Lieb.  Ann. 
298,  253  (1897)].  He  considers  that  the  aluminium  chloride 
splits  out  the  hydrogen  halide  from  the  alkyl  halide  forming 
in  this  way  an  olefin  which  is  added  to  the  aromatic  hydro- 
carbon. This  is  in  line  with  his  views  concerning  reactions 
of  carbon  compounds  in  general. 

In  conformity  with  the  general  principles  outlined  in 
previous  chapters  the  view  of  the  mechanism  of  the  Friedel- 
Crafts  reaction  which  will  be  adopted  here  will  be  that  of 
Menschutkin,  Boeseken,  and  Schmidlin  and  Lang,  based 
upon  the  formation  of  a  ternary  compound.  This  view 
brings  the  Friedel-Crafts  reaction  in  line  with  many  other 
organic  reactions,  and  permits  of  a  more  systematic  classi- 
fication of  the  various  types. 

In  the  Friedel-Crafts  reaction  then  it  may  be  assumed 
that  a  ternary  compound  consisting  of  aluminium  chloride 
and  the  two  reacting  components  is  formed  which  is  in 
equilibrium  with  various  sets  of  substances.  The  following 
example  will  illustrate  the  formulations: 


C2H4     ^+CeH.H+AlCla,  (a) 

C6H5H  \      rc2H4HCll       pR 

HCI     l=Uici3      J406116' 

''       [  HC1  1 


100  CHEMICAL  REACTIONS. 

In  this  reaction,  as  generally  viewed,  ethyl  benzene  is 
formed  from  ethyl  chloride,  benzene  and  aluminium  chlor- 
ide. Some  of  the  equilibria  in  this  reaction  with  the  ternary 
(or  considering  ethyl  chloride  to  be  made  up  of  ethylene 
and  hydrogen  chloride,  quarternary)  intermediate  com- 
pound are  indicated.  Only  a  few  of  the  possible  reactions 
are  shown.  Taking  equilibria  (a)  and  (c),  it  is  evident 
that  this  represents  the  reaction  as  ordinarily  viewed.  In 

[HOI  1 
A  ,pj  may  also  be  in  equilib- 
rium with  its  components.  If  acetyl  chloride  is  used  in 
place  of  ethyl  chloride,  a  binary  compound  of  acetophenone 
and  aluminium  chloride  is  formed  which  may  be  decomposed 
by  water.  The  presence  of  aluminium  chloride  in  the 
reaction  mixture  appears  to  favor  the  formation  of  con- 
densation products,  that  is,  more  complex  bodies  from  the 
simple  substances.  In  the  presence  of  aluminium  chloride 
the  products  of  certain  definite  equilibria  are  obtained. 
With  other  so-called  "condensing  agents"  or  catalysts,  such 
as  sulfuric  acid  or  sodium  hydroxide  in  place  of  aluminium 
chloride,  other  products  may  be  formed  due  to  other  of  the 
possible  equilibria  being  favored.  As 'indicated  in  Chapter 
V,  a  large  number  of  equilibria  and  products  are  possible 
with  a  ternary  compound.  The  part  that  a  substance  such 
as  aluminium  chloride  plays  in  such  reactions,  is  to  cause 
certain  definite  equilibria  to  dominate  over  others  as  already 
indicated.  Other  added  substances  would  cause  other 
equilibria  to  dominate.  For  instance,  if  alkali  were  added 
to  a  mixture  such  as  the  above,  the  reaction  by  which 
ethylene  and  hydrogen  chloride  is  formed  from  ethyl 
chloride  might  predominate.  While  there  are  definite 
differences  in  these  changes,  the  principle  which  is  brought 
out  is  that  with  a  certain  number  of  reacting  substances 
which  go  to  make  up  a  ternary  or  even  more  complex 
compound  and  which  is  in  equilibrium  with  a  large  number 


SOME  CHEMICAL  REACTIONS-  1Q1 


of  different  sets  of  products,  the  addition  of  a  new  substance 
to  the  reacting  mixture  will  cause  certain  of  the  reactions  or 
equilibria  to  predominate  over  others,  and. each  different 
added  substance  may  result  in  a  different  equilibrium  being 
observed  experimentally.  There  is  nothing  said  as  to 
whether  the  added  substance  acts  as  a  catalyst  or  not. 
This  question  is  evidently  a  secondary  one.  From  the 
theory  of  catalytic  actions  developed  in  Chapter  IV,  a 
reaction  is  catalytic  if  one  of  the  reacting  substances  appears 
as  an  initial  substance  and  final  product.  With  acetyl 
chloride,  benzene,  and  aluminium  chloride,  a  compound  of 
acetophenone  and  aluminium  chloride  is  obtained.  If  the 
reaction  is  considered  to  be  at  an  end  here,  aluminium 
chloride  may  be  considered  to  act  as  a  catalyst  since  its 
composition  is  unchanged.  If,  however,  water  is  added  to 
the  reaction  mixture,  as  is  generally  done  experimentally, 
then  the  aluminium  chloride  is  decomposed  and  would  not 
be  called  a  catalyst  in  the  reaction.  This  view  of  the 
function  of  the  action  of  aluminium  chloride  as  a  possible 
catalyst  in  the  Friedel-Crafts  reaction  holds  throughout. 
Whether  it  is  assumed  to  act  as  a  catalyst  depends  upon 
where  the  reaction  is  assumed  to  stop.  In  this  connection 
it  may  be  pointed  out  that  the  action  of  aluminium  chloride 
has  been  considered  by  some  from  two  points  of  view. 
Either  it  has  been  considered  to  act  catalytically  or  as  in 
an  ordinary  chemical  action  taking  part  in  a  definite 
stoichiometrical  ratio;  but  it  is  seen  that  this  difference  is 
more  one  of  definition  and  classification  than  a  real  difference 
in  the  mechanism  of  the  reaction. 

Since  there  is  definite  evidence  in  a  number  of  the  re- 
actions that  ternary  or  more  complex  intermediate  com- 
pounds are  formed,  and  there  is  evidence  of  complex 
compound  formation  with  a  number  of  other  compounds  of 
aluminium  and  similar  metal  halides,  the  general  explana- 
tion of  the  Friedel-Crafts  reaction  may  be  taken  to  be  that 


102  -CHEMICAL  REACTIONS. 


indicated  with  a  complex  compound  of  the  third  or  higher 
order  as  intermediate  compound.  The  readiness  with  which 
such  complex  compounds  are  formed  and  their  stabilities 
will  depend  evidently  upon  the  nature  of  the  reacting  sub- 
stances, and  it  should  be  possible  to  find  regularities  in  the 
compositions  of  these  reacting  substances,  upon  which  the 
ready  formation  of  the  condensation  products  in  this  re- 
action depends.  A  comparison  of  such  groupings  which 
facilitate  this  reaction  (either  by  more  rapid  formation  of 
intermediate  products  and  their  decompositi  n  in  certain 
directions,  or  in  shifting  the  equilibria,  or  in  some  other 
way),  with  the  groupings  which  facilitate  the  same  or 
other  condensation  reactions  in  the  presence  of  other 
catalytic  or  condensing  agents,  should  be  of  value  in  develop- 
ing the  general  theory  of  the  mechanism  of  such  reactions, 
of  which  the  Friedel-Crafts  reaction  has  been  chosen  as  a 
well-known  example. 

A  number  of  reactions  which  are  aided  or  accelerated  by 
aluminium  chloride  will  now  be  given.  Only  the  initial 
and  the  final  products  which  are  of  immediate  interest  will 
be  outlined.  The  probable  complex  intermediate  compound 
will  not  be  formulated  although  it  will  be  understood  to  be 
present  and  involved  in  the  different  equilibria  in  every 
case.  The  reactions  only  in  exceptional  cases  proceed 
quantitatively  as  indicated,  and  there  are  as  a  rule  a 
number  of  other  products  formed  in  the  reactions.  These 
will  not  be  indicated  here.  It  is  evident  that  a  careful 
quantitative  study  of  these  reactions  would  be  of  great 
value. 

1.  C2H6C1  +  C6H6  =  C6H5C2H5  +  HC1. 

2.  CH3COC1  +  C6H6          =  CH3COC6H5  +  HC1. 

3.  CHC13  +  3C6H6  =  CH(C6H5)3  +  3HC1. 

4.  OsNCCla  +  3C6H6         =  Q2NC(CflH6)3  +  3HC1. 

5.  C6H5CH2CH2COC1 

=  C6H4  -  CH2  -  CH2  -  CO  +  HC1.1 

1  F.  S.  Kipping,  Trans.  Chem.  Soc.  65,  480  (1894). 


SOME   CHEMICAL  REACTIONS.  103 


6.  CH3COC1  +  CHsCOCl  +  CH3COC1 

=  CH3COCH2COCH2COC1  +  2HC1.2 

7.  3C3H7COC1        _  _ 

=  C2H5.CH.CO.CH(C2H5),CO.CH(C2H5).C03 

+  3HC1. 

8.  (C6H5)3CC1  +  HOCH3 

=  (C6H5)3COCH3  +  HC14  (Etherification). 

9.  CH3C1  +  C6H5NH2.HC1 

=  C6H4(CH3)N(CH3)2  +  3HC14  (Alkylation  of 

amines). 

10.  C2H5Br  +  H2S  =  C2H5SH  +  HBr.5 

11.  2C6H5CH2C1  =  (C6H5)2C  :  C(C6H5)2  +  2HC1.6 

12.  CH2  :  CH2  +  C6H6        =  C6H5CH2.CH3.7 

13.  CH  •  CH  +  C6H6          =  C6H5CH  :  CH2.8 

14.  CN.CN  +  C6H6  =  CN.C(C6H5)  :  NH.6 

15.  CH2.CH2.CH2  +  C6H6  =  C6H5.CH2.CH2.CH3.9 

16.  C6H5.N  :  C  :  O  +  C6H6  =  C6H5.NH.CO.C6H5.9 

17.  C02  +  C6H6  =  C6H5COOH.6   (Vr 

18.  S02  +  C6H6  =  C6H5S02H.7 

19.  CO  +  C6H6  =  C6H5CH0.10 

20.  02  +  2C6H6  =  2C6H5OH.7 

21.  S  +C6H6  =  C6H5SH.7 

22.  R.CH(CH2)2.COO+  C6H6 

=  R.CH(OH)CH2.CH2.CO.C6H5.6 

23.  CHC1  :  CC12  +  CC14     =  CC13.CHC1.CC13.6 

24.  CHC1  :  CC12  +  CHC13  =  CHC12.CHC1.CC13.6 

2  A.  Combes,  C.  r.  103,  814  (1886);   Ann.  chim.  phys.  [6]  12,  199 
(1887);  F.  S.  Kipping,  Proc.  Chem.  Soc.  9,  208  (1893). 

3  A.  Combes,  C.  r.  103,  814  (1886). 

4  C.  Friedel  and  J.  M.  Crafts,  Ann.  chim.  [6]  I,  503  (1884). 

5  V.  A.  Plotnikoff,  J.  Chem.  Soc.  Abstr.  (1913)  I,  1295. 

6  H.  J.  Prins,  J.  pr.  Chem.  89,  14,  432  (for  further  references)  (1914). 

7  C.  Friedel  and  J.  M.  Crafts,  Ann.  chim.  [6]  14,  433  (1888). 

8  R.  Varet  and  G.  Vienne,  Bull.  Soc.  chim.  47,  918  (1887). 

9  S.  Krapivin,  Chem.  Zentralb.  (1910)  I,  1335. 

10  L.  Gatterman  and  J.  A.  Koch,  Ber.  30,  1622  (1897);   Lieb.  Ann. 
347,  347  (1906). 


104  CHEMICAL  REACTIONS. 

25.  C2H4  +  HX  =  C2H5X. 

26.  CoHsONO,  +  C6Hfi        =  C6H5NO2  +  C2H5OH.n 

27.  C5HnONO  +  C6H6        =  C6H5NO  +  CsHnOH.11 

28.  C1CH2CO2C2H5  +  C6H6 

=  C6H5C2H5  +  C1CH2COOH.4 

29.  C1CO2C2H5  +  C6H6       =  C6H5C2H5  +  HC1  +  CO2.4 

30.  C6H5CH3  +  PC13  =  C6H4(CH3)PC12  +  HC1.12 

31.  3CH3I  +  CHC13  =  CHI3  +  3CH3C113  (CH3C1  volatile). 

32.  2C6H6  =  C6H5.C6H5  +  H2. 


CO 


34-C6H0     +      Br,  C6H5Br      +      HBr 

The  first  striking  fact  in  these  reactions  is  the  large 
number  of  different  compounds  whose  reactions  are  ac- 
celerated by  aluminium  halides.  Not  all  reactions  which 
have  been  studied  are  included  in  this  list,  but  the  variety 
is  sufficiently  great  to  show  the  general  applicability  of  the 
reaction.  Those  given  may  be  divided  into  groups:  Re- 
actions 1  to  11  include  the  elimination  of  hydrogen  halide 
in  the  formation  of  the  condensation  product;  reactions  12 
to  25  include  direct  addition  of  the  components,  accelerated 
by  the  presence  of  aluminium  halide;  reactions  26  and  27 
show  that  nitrogen  compounds  may  be  included;  reactions 
28  and  29  that  with  certain  groupings,  in  place  of  the 
elimination  of  hydrogen  halide  as  the  dominant  reaction, 
different  groups  may  be  eliminated;  reaction  30  shows  a 
further  possibility;  while  reactions  31  to  33  are  in  reality 
oxidation-reduction  reactions  and  should  be  treated  in  a 
later  chapter  but  are  included  here  for  the  sake  of  complete- 
ness; and  reaction  34,  really  an  oxidation-reduction  reaction 
also,  is  included  to  show  the  action  of  halogenation.  A 
number  of  other  reactions  which  are  catalyzed  by  aluminium 

11  E.  Boedtker,  Bull.  Soc.  chim.  IV  (3)  726  (1908). 

12  A.  Michaelis  and  C.  Panek,  Ber.  13,  653  (1880). 

13  J.  W.  Walker,  J.  Chem.  Soc.  85,  1089  (1904). 


SOME   CHEMICAL  REACTIONS.  105 

chloride  but  which  are  in  reality  oxidation-reduction  re- 
actions in  the  sense  that  certain  atoms  in  the  molecules 
change  their  valence  or  state  of  oxidation,  may  be  men- 
tioned. For  example,  xylene  at  its  boiling  temperature 
with  the  addition  of  2  to  4  per  cent,  aluminium  chloride 
yields  12  per  cent,  toluene  and  also  benzene  and  poly- 
methylated  benzene  (F.  Fischer  and  H.  Niggeman,  Ber.  49., 
1475  (1916).  The  action  of  aluminium  chloride  on  petrol- 
eum was  studied  by  A.  Pictet  and  I.  Lercynska  (Bull.  soc. 
chim.  IV,  19,  326  (1916)).  Cyclohexane  was  found  to 
rearrange  in  part  to  methylpentamethylene  on  heating  to 
boiling  for  48  hours  in  the  presence  of  aluminium  chloride 
(I.  Aschan,  Lieb.  Ann.  324,  1  (1902)). 

In  addition  to  the  evidence  regarding  complex  addition 
compounds  already  given,  another  line  of  proof  may  be 
mentioned.  The  reacting  mixtures  in  the  Frie<lel-Crafts 
reaction  as  a  rule  develop  more  or  less  color,  starting  with 
colorless  compounds.  The  formation  of  colored  compounds 
in  the  case  of  somewhat  different  reactions  has  been  taken 
to  show  addition  compounds  [J.  Kendall,  Jour.  Amer. 
Chem.  Soc.  37,  149  (1915)  for  aldehyde  and  ketone  addition 
compounds  with  acids,  and  H.  Wieland  and  E.  Wecker,  Ber. 
43,  699  (1910)  as  forerunners  of  a  number  of  substitution 
reactions.] 

With  regard  to  the  chemical  constitutions  or  structures 
of  the  intermediate  addition  compounds,  not  much  can 
be  said.  The  element  which  appears  to  be  specifically 
responsible  for  the  formation  of  these  compounds  is  alumi- 
nium. Aluminium  salts  readily  form  "  onium  "  or  molecular 
compounds  or  compounds  of  the  second  and  higher  orders. 
The  occurrence  of  complex  aluminium  salts  in  nature,  such 
as  the  aluminium  silicates,  bauxite,  etc.,  shows  that  complex 
inorganic  aluminium  compounds  are  capable  of  existing 
and  are  apparently  extremely  stable.  The  complex  organic 
compounds  of  aluminium,  some  of  which  have  been  proven 


106  CHEMICAL  REACTIONS. 

to  exist  and  others  which  are  assumed  to  be  formed  in  the 
Friedel-Crafts  reaction,  parallel  these  inorganic  compounds. 
The  difference  between  the  two  sets  lies  in  the  tendency 
of  the  organic  part  of  the  compounds  to  reach  a  more 
stable  condition  and  the  velocity  with  which  this  condition 
is  attained.  Otherwise  the  two  sets  of  compounds  are 
similar.  Besides  the  fact  that  chemical  combination  is 
probably  due  primarily  to  the  ability  of  the  aluminium  to 
form  onium  compounds  under  the  given  conditions,  it  is 
difficult  to  say  more  at  present  with  regard  to  the  chemical 
structures  of  these  complex  intermediate  compounds. 

In  place  of  the  aluminium  chloride  used  in  the  Friedel- 
Crafts  reaction,  it  has  been  found  that  some  of  the  chemical 
changes  may  be  accelerated  by  the  addition  of  other 
catalysts  to  the  reaction  mixtures.  Anhydrous  zinc  chloride 
has  been  used  to  some  extent  in  this  way.  The  following 
reactions  are  a  partial  list  of  such  changes.  The  part 
played  by  the  zinc  chloride,  in  the  formation  of  the  probable 
complex  intermediate  compounds  and  the  equilibria  of  the 
latter  with  various  sets  of  products,  is  omitted  and  only 
the  main  reactions  or  changes  are  shown  just  as  in  the 
Friedel-Crafts  reaction. 
r  TT  j 


co 


CO 

37.    C6H5CCl3+2  C0H5N(CH3)2 


38.  C13CHO  +  5C6H  N(C2H5)2 

=  [(C2H5)2NC6H4]3C.CH[C6H4N(C2H5)2]2 

+  H20  +  3HC1. 

39.  C6H5CHO  +  CH3N02        =  C6H5CH  :  CHNO2  +  H2O. 


SOME  CHEMICAL  REACTIONS.  107 

40.  (CH3)2(C2H5)C(OH)  +  C6H5OH 

=  C4H9  <^)>  -  OH  +  H2O. 

OH  OH 

41.  CH3COOH  +  C   ^>  OH  =  CH3CO  <f  ~VoH-fH2O. 


42.  HCOOH  +  3C6H5OH       =  HCK  _          +  2H2O. 

-OH 


It  is  evident  that  zinc  chloride  is  almost  as  universal  a 
catalyst  for  such  reactions  as  aluminium  chloride,  and 
undoubtedly  it  would  be  found  experimentally  that  in 
many  of  the  Friedel-Crafts  reactions  zinc  chloride  would 
answer  as  well  as  aluminium  chloride. 

Concentrated  sulfuric  acid  is  also  employed  very  often 
in  such  condensation  reactions.  It  can  be  used  in  reaction 
36  as  well  as  zinc  chloride.  Other  reactions  in  which  it 
has  been  used  as  catalyst  are  as  follows  (formulated  in  the 
same  way  as  the  preceding  reactions) : 

43.  2C6H6  +  (CH30)2CH2   =  (C6H5)2CH2  +  2CH3OH. 

44.  2C10H8  +  CH2O  =  H2C(C10H7)2  +  -H2O. 


'NO 

45.  2C6H5N02  +  CH20       =  H2cC  X         2+  H2O 

V>-N02 

46.  C6H5CHO  +  2QH6       =  CH(C6H5)3  +  H2O. 

47.  /OH 

C6H4-CHO  +  CH3COCH2C1 

yOH 

=  C6H4-CH  :  CH.COCH2C1  +  H2O. 

Other  catalysts  or  so-called  condensation  agents  may  be 
considered  in  the  same  way.  Without  elaborating  further, 
it  may  be  said  that  the  same  principles  apply  to  all  these 
reactions;  the  formation  of  a  complex  intermediate  addition 


108  CHEMICAL  REACTIONS. 

product  which  may  be  in  equilibrium  with  various  sets  of 
products,  and  the  course  of  the  reaction  -in  the  presence  of  a 
definite  catalyst  being  dependent  upon  the  concentrations 
of  the  various  reacting  substances  according  to  the  principle 
of  mass  action  and  the  relative  velocities  of  the  reactions 
if  equilibrium  has  not  been  attained.  In  a  number  of  cases 
the  intermediate  compound  has  been  isolated.  The  reac- 
tions are  quantitative  only  in  exceptional  cases.  As  a  rule 
a  number  of  products  are  obtained,  but  those  given  in  the 
above  equations  represent  the  products  which  were  of  in- 
terest at  the  time  the  reaction  was  studied. 

It  will  have  been  observed  that  a  certain  awkwardness  in 
nomenclature  has  occurred  in  the  discussion  of  the  reac- 
tions. In  the  formulations  of  the  different  reactions,  equi- 
libria have  been  spoken  of  at  times  without  the  intention  of 
conveying  the  meaning  that  the  various  substances  taking 
part  existed  at  definite  equilibrium  concentrations.  The 
term  equilibrium  was  used  in  these  cases  in  place  of  the 
more  usual  "  chemical  equation"  to  emphasize  the  signifi- 
cance of  reversibility  and  mass  action  effect. 

A  definite  group  of  reactions  which  has  been  studied 
extensively  is^  that  in  which  a  nitro-group  is  introduced 
into  an  organic  compound,  combined  with  carbon  and  in 
place  of  a  hydrogen  atom.  This  reaction  is  commonly 
known  as  nitration,  but  in  conformity  with  the  general 
chemical  nomenclature  it  should  be  called  nitronation. 
However,  for  the  present  in  this  book,  the  older  term 
nitration  will  be  used.  Before  taking  up  nitration  reactions 
in  detail,  some  general  relations  developed  in  the  reactions 
already  considered  and  some  additional  ones  will  be  dis- 
cussed briefly. 

It  is  well  known  that  the  presence  of  certain  side  chains 
on  the  benzene  nucleus  facilitates  the  introduction  of 
various  substituent  groups  in  place  of  the  hydrogen  of  the 
benzene  nucleus.  This  is  true  for  the  Friedel- Crafts  re- 


SOME  CHEMICAL  REACTIONS.  109 

action,  halogenation,  sulfonation,  nitration,  etc.  The  ques- 
tion of  the  possible  relation  of  this  phenomenon  to  the 
mechanism  of  the  reactions  has  been  studied  more  carefully 
in  nitration  than  in  other  reactions. 

It  has  been  found  that  aniline,  phenol,  and  similar  com- 
pounds of  this  type  are  nitrated  to  a  greater  extent  by  a 
given  strength  of  nitric  acid  than  is  benzene  itself.  It  has 
been  observed  quite  frequently  that  an  intermediate  com- 
pound is  formed  in  which  a  hydrogen  of  the  amino  or 
hydroxyl  group  on  the  benzene  ring  has  been  replaced  by 
the  nitro  or  other  entering  group.  This  compound  then 
rearranges  under  certain  conditions  so  that  the  entering 
group  substitutes  in  the  ortho  or  para  position.  Such 
rearrangements  are  very  general  and  were  first  studied 
systematically  for  the  rearrangement  of  hydrazobenzene 
to  benzidine.  This  type  is  therefore  commonly  known  as 
the  benzidine  rearrangement.  The  question  has  been  con- 
sidered whether  such  intermediate  compounds  always  occur 
in  the  nitration,  etc.,  of  derivatives  of  benzene  when  ortho 
and  para  derivatives  are  obtained,  or  whether  substitution 
in  the  ortho  and  para  positions  can  take  place  directly. 
This  led  to  the  development  of  two  theories  of  substitution: 
(1)  Direct  substitution,  which  takes  place  with  benzene 
compounds  having  an  amino  or  hydroxyl  group  already 
present;  (2)  Indirect  substitution,  which  always  occurs 
when  ortho  and  para  compounds  are  formed.  Holleman 
carried  out  a  serie  of  experiments  to  test  these  views,  and 
came  to  the  conclusion  that  it  is  not  essential  for  an  inter- 
mediate compound  such  as  is  assumed  in  indirect  substitu- 
tion to  be  formed,  and  that  indirect  and  direct  substitution 
are  essentially  the  same. 

In  discussing  this  question,  it  seems  simplest  to  look 
upon  it  as  analogous  to  the  etherification  of  alcohol  with 
sulfuric  acid  as  catalyst.  In  this  reaction,  it  has  been 
suggested  that  the  etherification  takes  place  in  several 


110  CHEMICAL  REACTIONS. 

steps;  first  the  formation  of  ethyl  hydrogen  sulfate,  and 
then  the  action  of  more  alcohol  with  the  latter  to  form 
ether.  The  evidence  adduced  by  those  holding  this  view 
is  that  ether  can  be  formed  by  starting  with  ethyl  hydrogen 
sulfate  and  that  ethyl  hydrogen  sulfate  can  be  formed  from 
ethyl  alcohol  and  sulfuric  acid,  and  therefore  that  the  ethyl 
hydrogen  sulfate  is  an  intermediate  product  which  is  always 
formed.  It  has  been  pointed  out  in  a  previous  chapter 
however  that  a  more  correct  view  of  this  reaction  is  that 
the  ethyl  alcohol  and  sulfuric  acid  form  an  addition  com- 
pound which  can  dissociate  in  different  ways  and  is  there- 
fore in  equilibrium  with  various  sets  of  products;  for 
example,  to  form  ethyl  hydrogen  sulfate  in  one  reaction; 
ether  in  another,  olefin  in  another,  and  so  on.  The  product 
actually  obtained  depends  upon  the  conditions  (chemical 
and  physical)  as  already  pointed  out. 

It  seems  that  the  question  of  indirect  substitution  is  a 
similar  one  and  that  here  also  an  intermediate  addition 
compound  is  formed  which  may  dissociate  on  the  one  hand 
to  form  a  compound  with  the  substituent  in  the  side  chain, 
and  on  the  other  hand  with  the  substituent  in  the  benzene 
nucleus. 

In  taking  up  a  more  detailed  study  of  nitration,  the 
general  methods  of  preparing  nitro  compounds  may  first 
be  mentioned.  The  usual  methods  involve  the  action  of 
nitric  acid  alone,  or  in  the  presence  of  sulfuric  acid,  or  of 
water,  or  of  a  non-ionizing  medium  such  as  ether.  Other 
methods  involve  the  use  of  ethyl  nitrate  or  of  nitrosulfates 
(NO2.OSO2.OH),  nitroacetates  (or  acetyl  nitrate),  etc.  For 
methods  used  in  isolated  cases  reference  must  be  made  to 
the  books  of  Weyl,  Lassar-Cohn,  and  others. 

J.  U.  Nef's  view  of  nitration  is  of  interest.  He  considers 
the  reaction  to  be  analogous  to  an  aldol  condensation  and 
formulates  it  as  follows  (Jour.  Amer.  Chem.  Soc.  26,  1566 
(1904)): 


SOME   CHEMICAL  REACTIONS.  Ill 


f^ 
U 


His  general  theory  for  this  and  similar  reactions  may 
be  given  in  his  own  words:  "  Excluding  reactions  called 
ionic,  a  chemical  reaction  between  two  substances  always 
first  takes  place  by  their  union  to  form  an  addition  product. 
The  one  molecule  being  unsaturated  and  in  a  partially  active 
condition  absorbs  the  second  molecule  because  it  partially 
splits  or  dissociates  it  into  active  portions.  The  resulting 
addition  product  then  often  dissociates  spontaneously, 
giving  two  new  molecules.  The  similarity  of  such  reactions 
to  those  called  ionic  is  at  once  apparent,  but  their  relation- 
ship cannot,  in  the  present  state  of  our  knowledge,  be 
clearly  understood."  Nef's  view  of  this  reaction  is  similar 
to  the  one  developed  here  and  differs  mainly  in  that  he 
formulates  the  manner  in  which  the  hydrogen  atom  of  the 
benzene  acts  specifically. 

Nitro  compounds  may  be  obtained  by  the  action  of  ethyl 
nitrate  and  aluminium  chloride.  Since  many  of  the  Friedel- 
Crafts  reactions  may  be  carried  out  with  sulfuric  acid  in 
place  of  aluminium  chloride,  and  since  in  nitration  with 
nitric  acid,  sulfuric  acid  is  very  often  used,  the  fact  is 
brought  out  again  that  nitration  belongs  to  the  same 
general  type  of  reaction  as  the  Friedel-Crafts  reaction. 
This  similarity  may  be  brought  out  in  the  following  manner. 
The  reaction 

/R       C6H5\  /R 

2C6H5  +  O  =  C-R  ""*  C6H5-C-R  +  H2O 
(A)  (B) 

is  accelerated  either  by  sulfuric  acid  or  aluminium  chloride 
In  the  compound  (B)  the  oxygen  atom  plays  the  part  of  the 
chlorine  in  the  usual  Friedel-Crafts  reaction.  If  in  place 
of  the  oxygen  compound,  the  ketone,  B,  the  oxygen  com- 
pound nitric  acid  be  substituted,  the  reaction  would  be 
similar.  The  same  is  true  if  (B)  represented  an  aldehyde. 


112  CHEMICAL  REACTIONS. 

Such  reactions  with  aldehydes  were  illustrated  in  reactions 
44  to  47  above  where  sulfuric  acid  was  the  special  catalyst. 
Reaction  26  illustrated  nitration  with  ethyl  nitrate  and 
aluminium  chloride.  Remembering  the  fact  that  in  the 
final  product  condensation  has  taken  place  with  the  elimina- 
tion of  the  oxygen  of  the  ketone,  aldehyde,  or  nitric  acid, 
whether  the  catalyst  was  sulfuric  acid  or  aluminium 
chloride,  and  comparing  the  initial  and  final  products 
obtained  with  the  initial  and  final  product  of  the  reaction 
when  a  base  is  neutralized  by  an  acid; 

HX  +  BOH  =  BX  +  H20 

it  is  evident  that  the  benzene  plays  the  part  of  the  acid, 
and  the  ketone,  aldehyde,  or  nitric  acrd  that  of  the  base. 
In  discussing  the  entrance  of  a  new  substituent  in  a  ben- 
zene derivative,  it  will  be  found  that  a  number  of  reactions 
can  be  very  much  simplified  if  it  is  considered  that  the  para 
(or  ortho)  hydrogen  atom  to  the  group  present  takes  part 
in  the  reaction.  To  explain  by  means  of  an  example :  In 
aniline  it  may  be  assumed  that  an  equilibrium  exists  be- 

-8 

tween  the  two  tautomeric  forms  (^ j  NH2 

(A)  ~lB) 

In  (B)  the  nitrogen  is  in  the  onium  form,  and  the  benzene 
nucleus  (or  more  strictly,  the  para  carbon  atom)  plays  the 
part  of  the  acid.  This  equilibrium  is  similar  to  the  one  pres- 

I! 
ent  in  glycine;    namely,  H02C.CH2.NH2^  p.OC.CH8.NH8 

There  is  evidence  to  show  that  the  equilibrium  exists  in  the 
latter  case.  In  the  former,  the  assumption  of  such  a 
similar  equilibrium  helps  to  explain  a  number  of  reactions, 
in  fact,  it  may  be  taken  to  be  the  fundamental  phenomenon 
in  all  "benzidine  rearrangements." 


SOME  CHEMICAL  REACTIONS.  113 

Taking  the  simplest  case,  the  nitration  of  benzene,  the 
reaction  may  be  formulated  as  follows: 

OH 

HO.NO, 

'H 


NH< 


02N 


NH-N02 

+  H20 

These  equilibria  represent  a  more  or  less  ideal  case,  since 
as  a  rule  other  substances  are  present,  and  also  the  nitro- 
amine  which  may  be  formed  reacts  farther.  If  sulfuric 
acid  is  present,  a  ternary  intermediate  compound  would 
be  formed.  If  acetanilide  were  used  instead  of  aniline, 
the  general  reaction  would  be  similar.  If,  however,  a 
large  excess  of  sulfuric  acid  were  used  in  the  reaction,  then 
the  aniline  would  be  present  practically  entirely  as  aniline 
sulfate  and  there  would  not  be  the  tautomeric  form  present. 
Under  these  circumstances,  the  intermediate  compound 
would  not  be  the  same  as  before,  and  the  nitration  would 
proceed  as  if  benzene  itself  were  being  nitrated.  Mainly 
meta  compound  would  be  obtained  under  these  conditions. 
The  velocity  of  nitration  of  benzene  derivatives  containing 
different  substituents  was  studied  by  H.  Martinsen  [Z. 
physik.  Chem.  50,  385  (1905);  59,  605  (1907)].  Rewound 
the  velocities  to  be  dependent  upon  the  substituents  in  the 
following  way: 

NQ2<S03H<CQ2H<C1<  CH3<OCH3<  OC2H5<  OH. 
Smaller  velocity  greater  velocity 


114  CHEMICAL  REACTIONS. 

Those  groups  which  when  present  diminish  the  velocity 
orient  the  nitro  group  into  the  meta  position,  those  which 
increase  the  velocity  orient  the  nitro  group  into  the  para 
and  ortho  positions.  A  reason  for  the  increase  in  the 
velocity  of  substitution  by  amino  and  hydroxyl  groups 
may  well  be  due  to  the  unsaturation  of  these  groups  and 
their  ability  to  form  addition  compounds.  The  nitro, 
sulfonic  acid,  etc.,  groups  being  more  saturated,  have  the 
opposite  effect. 

In  the  nitration  in  the  presence  of  sulfuric  acid,  W. 
Markownikoff  [Ber.  32,  144  (1899)]  and  others  consider 
the  nitrating  agent  to  be  nitrosulfuric  acid, 

^OH 

SO2 

— ON02. 

In  the  presence  of  acetic  anhydride  or  acetic  acid,  a  similar 
compound  of  nitric  and  acetic  acids,  acetyl  nitrate,  is 
assumed  [A.  Pictet  and  P.  Genequand,  Ber.  35,  2526  (1902)], 
arid  with  benzoic  acid,  benzoyl  nitrate  [R.  Willstatter, 
Ber.  42,  4152  (1909)].  Whether  these  compounds  play 
the  part  assigned  is  similar  to  the  question  of  whether  ethyl 
sulfuric  acid  is  always  formed  in  the  preparation  of  ether, 
and  may  be  handled  similarly.  If  it  is  formed  at  some 
stage  of  the  reaction,  it  will  probably  be  more  able  to  form 
an  addition  compound,  since  it  is  obtained  by  loss  of  the 
elements  of  water  from  two  other  molecules  and  is  probably 
more  unsaturated.  In  this  way,  the  velocity  of  the  reaction 
might  be  accelerated,  but  an  intermediate  addition  com- 
pound would  still  be  formed. 

Nitration  in  solvents  other  than  water  is  to  be  preferred 
at  times.  In  acetic  acid  for  example,  besides  the  advantages 
just  spoken  of,  the  solvent  effect  of  the  acetic  acid  may  be 
of  aid  in  increasing  the  concentration  of  the  hydrocarbon. 
Such  conditions  as  the  hydrogen  ion  concentration  of  the 
mixture  may  also  play  a  part  and  may  be  influenced  favor- 


SOME   CHEMICAL   REACTIONS.  115 

ably  by  changing  the  solvent.  Another  factor  to  be  con- 
sidered is  that  in  some  reactions  nitric  acid  will  cause  oxida- 
tion, and  the  choice  of  the  solvent  will  sometimes  obviate 
this.  These  special  cases  have  not  as  yet  been  investigated 
quantitatively  with  sufficient  care  to  enable  general  con- 
clusions to  be  drawn  as  to  the  reasons  for  these  conditions. 
Aliphatic  nitro  compounds  cannot  as  a  rule  be  prepared 
in  the  same  way  as  the  aromatic  nitro  compounds.  The 
more  rapid  oxidation  of  aliphatic  hydrocarbons  by  nitric 
acid  is  the  main  interfering  factor,  so  that  conditions  must 
be  chosen  which  minimize  oxidation  and  promote  nitration. 
The  oxidation  reactions  are  of  such  complexity  in  these 
cases  that  no  attempt  will  be  made  to  formulate  them. 
Only  a  summary  of  the  conditions  favoring  nitration  will 
be  given.  The  use  of  a  solvent  such  as  ether  for  carrying 
out  the  reaction  is  often  successful.  Also  dilute  nitric  acid 
has  been  used,  and  alkyl  (generally  ethyl)  nitrate.  In  the 
Friedel-Crafts  reaction  with  ethyl  nitrate,  aluminium  chlor- 
ide is  used  as  catalyst.  In  aliphatic  nitrations  with  ethyl 
nitrate,  alkalis  such  as  metal  alkoxides  (NaC^Hs)  are 
found  to  be  best.  The  use  of  alkalis  brings  out  the  simi- 
larity of  this  reaction  to  aldol  condensations  which  are 
also  favored  by  alkalis.  An  example  of  aliphatic  nitration, 
in  comparison  with  an  aromatic  one  may  be  given: 


_  v  __  —  COCHs 

C2H5ON02+H2C  NO2CH  +C2H5OH, 


C2H6ONO2+H.C6H6  "  NO2C6H5+C2H5OH. 


The  presence  of  unsaturated  or  so-called  "negative"  groups 
on  the  carbon  atom  being  nitrated  appears  to  be  necessary 
for  a  satisfactory  carrying  out  of  the  reaction. 

Another  method  for  the  aliphatic  nitration  is  the  reaction 
of  alkyl  halide  with  silver  nitrite,  in  which  considerable 
nitro  compound  is  formed.  With  alkali  nitrite  on  the  other 
hand,  very  little  nitro  compound  is  formed.  This  difference 


116  CHEMICAL  REACTIONS. 

is  evidently  due  to  the  different  oxidizing  potentials  of  the 
silver  and  the  alkali,  and  the  equilibria  between  various 
sets  of  products  and  the  intermediate  addition  compound. 
Similar  questions  come  up  with  other  sets  of  isomeric  com- 
pounds, cyanides  and  isocyanides;  oxygen  and  nitrogen 
ethers  of  cyanic  acid,  etc.  This  question  will  be  taken  up 
again  in  a  later  chapter. 

While  the  explanation  of  the  benzidine  rearrangement 
has  been  applied  specifically  to  nitration  only,  it  evidently 
holds  for  all  similar  reactions.  With  benzidine,  the  formula- 
tion may  be  given  as  follows : 


(A)  — ^  (B) 

>-NH2—  NH£-< 


(C) 

Equilibrium  may  exist  between  the  three  compounds  (A), 
(B),  and  (C).  In  the  presence  of  strong  acid  or  other 
suitable  catalytic  agent,  complex  additions  of  (A),  (B), 
and  (C)  with  the  former  may  take  place,  and  these  may 
then  decompose  in  different  directions,  giving  in  addition 
to  (A),  (B),  and  (C),  compounds  such  as 


(D)  (E) 

etc.  The  conditions  of  the  reaction,  such  as  the  formation 
of  more  stable  salts  from  the  sulfuric  acid  and  (D)  or  (E) 
may  control  the  yield  of  the  different  products  obtained, 
and  in  this  way,  (E)  would  be  obtained  from  (^4). 

The  formation  of  diazo  compounds  may  be  taken  up 
briefly.     First    the    reactions    in    which    no    hydrocarbon 


SOME  CHEMICAL  REACTIONS. 


117 


radicals  are  present  will  be  described.  It  will  be  recalled 
that  in  the  formation  of  amides  the  reaction  was  treated 
in  the  same  way  as  the  formation  of  esters  from  acids  and 
alcohols; 

AOH  +  HNH2  =  ANH2  +  H2O, 
or 


AH 


H2O 


HO  I       TAH1 

H2°      LNHSJ 


H20. 


.NH3J 


The  same  principle  can  be  used  to  explain  the  formation  of 
amides  of  nitric  and  nitrous  acids  (or  the  formation  of 
nitroamines  and  diazotization).  If  A  =  NO2,  then 


02NOH  +  NH3  =  O2NONH4  = 
or 


and  if  A  =  NO 


NH3 


O2NNH2 

or 
[N20  +  H2O] 


H2O, 


ONOH  +  NH3  =  ONONH4  =     ONNH2 

[N2  +  H20] 


H2O. 


The  nitroamine  and  nitrosoamine  are  unstable  under  ordi- 
nary conditions  (since  nitrogen  apparently  does  not  possess 
the  inertia  of  carbon),  differing  in  this  way  from  the  nitro- 
derivatives  of  the  hydrocarbons.  Nitroamine,  known  often 
as  nitramide,  or  its  tautomer,  hyponitrous  acid,  decomposes 
readily  into  nitrous  oxide  and  water,  while  nitrosoamine 
forms  nitrogen  and  water  (analogous  to  diazo  compounds). 
It  was  pointed  out  in  the  Friedel-Crafts  reaction  that 
the  hydroxyl  group  or  a  chlorine  atom  might  be  eliminated 
in  the  condensations;  for  example, 


or 


ROH  +  HC6H5^RC6H5  +  H2O, 
RC1  +  HC6H5^RC6H5  +  HC1. 


Similarly  with  the  reactions  with  ammonia, 

AOH  +  HNH2e-^ANH2  +  H2O, 


118  CHEMICAL  REACTIONS. 

or 

AC1  +  HNH2*^ANH2  +  HC1. 

The  action  of  nitrosyl  chloride  on  ammonia  is  similar; 
namely, 

ONOH  +  HNH2=^ONNH2  +  H2O, 
and 

ONC1  +  HNH2s^ONNH2  +  HC1. 

The  action  of  nitrous  acid  on  amines  is  indicated  very 
often  as  follows  :  *  '* 

RNH2  +  ONOH^-^RN2OH  +  H2O. 


In  looking  at  this  reaction  from  the  point  of  view  of  inter- 
mediate addition  compound  formation,  it  is  evident  that 
it  belongs  to  the  same  group  of  reactions.  The  intermediate 

addition   compound   might   be    formulated         "  *Q^QJ| 

and  the  following  components  can  be  recognized  and  would 
be  present  in  the  various  equilibria, 

H20,  olef.HOH,  RNH2,  HNO2,  NH3,  etc. 

The  diazotization  reaction  may  also  be  formulated  simi- 
larly to  the  action  of  a  base  on  an  acid  : 

BOH  +  HA  =  BA  +  H20, 
ONOH  +  HNHR  =  ONNHR  +  H2O. 

With  nitrosyl  chloride  or  ethyl  nitrite  in  place  of  nitrous 
acid,  the  same  holds  except  for  Cl  or  OC2H5  instead  of  OH. 
The  nitrous  acid  in  this  reaction  corresponds  to  the  base, 
and  the  amine  to  the  acid.  This  formulation  also  shows 
how  general  a  classification  may  be  developed  from  a 
simple  scheme  and  that  although  the  reactions  of  organic 
chemistry  appear  to  be  most  complex  and  different,  in 
reality  a  great  many  conform  to  simple  fundamental  prin- 
ciples and  changes.  If  A  =  C6H5,  then  the  reaction  corre- 
sponds to  the  formation  of  nitrosobenzene,  etc. 


SOME  CHEMICAL  REACTIONS.  119 

It  has  been  noticed  that  in  some  reactions  the  part  played 
by  alcohols  corresponds  to  the  part  played  by  the  acid,  HA; 
for  instance,  in  the  formation  of  esters  from  acid  chlorides 
and  alcohols,  in  the  type  reaction 

BX  +  HA  =  BA  +  HX. 

This  corresponds  to  the  neutralization  reaction  just  given 
except  that  X  is  used  in  place  of  the  OH.  The  general 
principle  of  intermediate  compound  formation,  though  not 
mentioned  every  time,  must  be  understood  to  apply  to  all 
these  reactions.  If  nitrous  acid  plays  the  part  of  BX 
and  an  alcohol  that  of  HA,  then  the  ready  formation  of 
nitrite  esters  is  not  surprising  when  the  two  interact.  From 
this  point  of  view  the  nitrite  esters  are  the  aquo-esters  of 
nitrous  acid,  and  diazo  compounds  are  the  ammono-esters 
of  nitrous  acid,  ON.OR  and  ON.NHR  (not  considering 
tautomeric  rearrangements  within  the  molecule). 


CHAPTER  VII. 

SOME  CHEMICAL  REACTIONS   (CONTINUED). 

THE  discussion  of  the  mechanism  of  the  reactions  con- 
sidered so  far  may  be  summarized  as  follows: 

(1)  Reactions  occurring  in  organic  chemistry  are  similar 
to  those  in  inorganic  chemistry. 

(2)  The  theory  of  reactions  in  aqueous  solutions,  hereto- 
fore based  upon  ionization  relationships,  can  be  accounted 
for  by  addition  compound  formation  involving  the  solvent. 

(3)  All  reactions  appear  to  take  place  through  the  inter- 
mediate formation  of  an  addition  compound.     If  the  re- 
action is  catalytic,  the  catalyst  is  one  of  the  components  of 
the  addition  compound. 

(4)  When  water  is  considered  as  the  catalyst  for  reactions 
taking  place  in  aqueous  solutions,  the  hydrates  formed  may 
give  rise  to  ionization. 

The  reactions  may  be  based  upon  the  general  equation: 

BX  +  HA  =  BA  +  HX. 
They  may  be  grouped  in  outline  as  follows: 

I.  Neutralization    of    an    acid    by    a    base;     B  =  metal, 

X  =  OH,  A  =  acid  group. 

NH40H  +  HC1  =  NH4C1  +  H20, 
NaOH  +  HC1  ^  NaCl  +  H20. 

Water  may  act  as  the  catalyst  in  these  reactions. 

II.  Friedel-Crafts    reaction;     B  =  R,     X  =  Cl    or    OH, 

A  =  C6H5,  etc. 

RCl+HPh  =  RPh  +  HCl, 
ROH  +  HPh  =  RPh  +  H20. 

120 


SOME  CHEMICAL  REACTIONS.  121 

Aluminium  chloride,  zinc  chloride,  sulf  uric  acid,  hydrogen 
chloride,  etc.,  may  act  as  the  catalyst. 

III.  Aldol  condensation;  BX  =  aldehyde  or  ketone,  A  =  so- 

called  "negative"  group  combined  with  a-carbon 
atom. 

RC  =  O  +  H2CA2  =  RCH  :  CA2  +  H20. 
H 

Various    catalysts;    zinc    chloride,    hydrogen    chloride, 
alkalies,  etc. 

IV.  Esterification;    B  =  alkyl,   A  =  acid  group,   X  =  Cl 

or  OH. 

ROH  +  HA  =  RA  +  H2O, 
RC1  +  HA  =  RA  +  HC1. 

Catalysts;  zinc  chloride,  sulf  uric  acid,  hydrogen  chloride, 
etc. 

V.  Etherification;  B  =  alkyl,  A  =  alkoxyl  group,  X  =  Cl 

or  OH. 

ROH  +  HOR'  =  ROR'  +  H20, 
RC1  +  HOR'  =  ROR'  +  HC1. 

Catalysts  as  in  reactions  IV. 

VI.  Amide  formation;    B  =  acyl  group,  X  =  OH  or  Cl, 

A  =  amino  group. 

AcOH  +  HNH2  =  AcNH2  +  H2O, 
AcCl  +  HNH2  =  AcNH2  +  HC1, 
AcOH  +  HNRs  =  AcNR,  +  H2O. 


VII.  Amine  formation;   B  =  alkyl  or  aryl  group,  X  =  Cl 
or  OH,  A  =  amino  group. 

ROH  +  HNH2  =  RNH2  +  H2O, 
RC1  +  HNH2  =  RNH2  +  HC1, 
ROH  +  HNR/  =  RNR2'  +  H2O. 


122  CHEMICAL  REACTIONS. 

VIII.  Formation  of  nitro  compounds;  B  =  N02,  X  =  OH 

or  substituted  OH  group,  A  =  alkyl  or  aryl  group. 

O2NOH  +  HC6H5  =  O2NC6H5  +  H2O, 
O2NOC2H5  +  HC6H5  =  O2NC6H5  +  C2H5OH, 
O2NOSO2OH  +  HC6H5  =  O2NC6H5  +  H2SO4, 
O2N02CCH3  +  HC6H5  =  O2NC6H5  +  HO2CCH3. 

IX.  Formation  of  nitroso  compounds;  B  =  NO,  X  =  OH, 

Cl,  or  substituted  OH  group,  X  =  alkyl  or  aryl  group. 
ONOH  +  HC6H5  =  ONC6H5  +  H2O, 
ONC1  +  HC6H5  =  ONC6H5  +  HC1, 
ONOC2H5  +  HC6H5  =  ONC6H6  +  C2H5OH. 

X.  Diazotization;    B  =  NO,  X  =  OH  or  Cl,  A  =  amino 

or  alkylated  or  arylated  group. 

ONOH  +  HNHR  =  ON2HR  +  H2O, 
ONC1    +  HNHR  =  ON2RH  +  HC1. 

XI.  Benzidine   rearrangement;     B  =  NO2,    X   and   A  = 

NHC6H4. 

H 

I 


-  NH  -  C6H4H  =  NH  -  C6H4  -  N02. 

Catalysts:   sulfuric  acid,  phosphorus  pentachloride,  etc. 

These  examples,  while  by  no  means  complete,  show  how 
general  the  given  type  of  reaction  is,  and  that  many  of  the 
apparently  different  groups  of  reactions  of  organic  chem- 
istry may  be  classed  together  and  treated  from  one  general 
point  of  view.  Some  general  relations  may  be  developed 
from  these  equations.  The  formation  of  certain  products 
in  any  given  case  depends  as  stated  repeatedly  upon  equi- 
librium relationships,  velocities  of  the  different  reactions, 
and  concentrations  of  the  various  substances  involved. 
Taking  any  one  set  of  reactions,  it  would  be  possible  to 
develop  regularities  with  regard  to  various  groups  present 


SOME  CHEMICAL  REACTIONS.  123 

in  the  reacting  molecules  and  the  products  obtained.  To 
attempt  to  do  this  here  would  lead  too  far  from  the  main 
questions  which  it  is  desired  to  present.  At  the  present 
time,  comparable  quantitative  data  with  regard  to  the 
relative  velocities  of  various  reactions  are  not  at  hand. 
In  fact,  quantitative  measurements  of  very  few  organic 
reactions  are  available,  so  that  it  is  evident  that  such  a 
comparison  of  the  constitutional  factors  upon  which  the 
formation  of  certain  sets  of  products  in  reactions  apparently 
dissimilar  but  fundamentally  belonging  to  the  same  type, 
is  not  possible  at  present.  This  however  does  not  apply 
to  the  possibility  of  such  studies  in  isolated  groups  of  com- 
pounds. For  one  thing,  it  is  only  necessary  to  refer  to 
Holleman's  work  on  the  substitution  derivatives  of  benzene 
and  benzene  derivatives,  to  indicate  the  nature  of  the  work 
which  may  be  done  in  systematizing  such  reactions.  The 
velocities  of  esterification  of  substituted  acids  and  alcohols 
also  offer  a  large  field  where  much  systematic  work  has 
already  been  done  and  many  new  and  interesting  relations 
have  been  developed. 

There  is,  however,  one  set  of  relations  which  appears  of 
interest  in  comparison  with  reactions  of  inorganic  chemistry. 
It  will  have  been  noticed  that  in  the  general  reaction 

BX  +  HA  =  BA  +  HX, 

the  velocities  of  the  reactions  of  the  hydrogen  compounds, 
HA,  vary  with  the  character  of  A  just  as  do  the  strengths  or 
ionization  constants  of  organic  and  inorganic  acids.  It  has 
been  customary  for  some  years  now  to  attribute  the  re- 
actions of  many  inorganic  substances  in  solutions  to  the 
presence  of  ions,  and  the  primary  reason  for  the  reactions 
and  their  great  velocities  to  certain  properties  of  the  ions. 
In  Chapter  III  it  was  shown  in  the  development  of  the 
theories  of  the  structures  of  acids,  how  the  ionic  theory 
played  an  important  part  in  the  evolution  of  the  subject, 


124  CHEMICAL.  REACTIONS. 

and  that  at  present,  the  view  of  acids  is  based  upon  an 
outgrowth  of  the  ionic  theory  and  included  in  the  modern 
views  of  Werner.  Similar  relations  may  be  shown  to  hold 
for  organic  reactions  where  there  has  been  no  evidence  of 
ionization  as  the  term  is  accepted  in  the  theory  of  electro- 
lytic dissociation. 

If,  in  the  above  general  reaction,  A  of  HA  represents  an 
alkyl  group,  the  activity  of  the  compound  HA  is  very  small 
ordinarily.  By  activity  in  this  connection  is  meant  the 
amount  of  reaction  in  a  definite  time.  It  is  used  in  a  very 
rough  qualitative  sense  here,  as  general  quantitative  com- 
parisons are  not  possible  at  present.  If,  into  the  alkyl 
group  are  introduced  in  place  of  the  hydrogen  atoms  acid 
groups,  so-called  negative  groups,  then  the  activity  of  the 
compound  increases  in  the  same  way  that  the  ionization 
constant  or  strength  of  an  acid  in  aqueous  solution  is 
increased  when  similar  groups  are  substituted  for  the 
hydrogen  atoms  of  the  a-carbon  atom  of  the  acid.  In  the 
former  case  however,  ionization  according  to  its  present 
definition  need  not  be  apparent.  If  HA  represents  an 
aromatic  hydrocarbon,  the  introduction  of  these  negative 
groups  exerts  an  opposite  effect  to  that  which  is  noted  if 
they  are  introduced  into  an  aliphatic  hydrocarbon,  the 
former  being  especially  marked  when  the  negative  group  is 
in  the  ortho  or  para  position  to  the  H  of  HA.  On  the  other 
hand,  with  the  so-called  positive  groups  OH,  NH2,  OR,  etc., 
in  the  ortho  or  para  position  to  the  H  of  an  aromatic  HA, 
the  HA  corresponds  in  reaction  velocity,  etc.,  to  a  stronger 
or  more  highly  ionized  acid,  while  if  HA  is  an  aliphatic 
hydrocarbon  the  groups  have  the  opposite  effect.  If  B 
in  BX  represents  an  aromatic  group  such  as  (CeHsCH)  =  O, 

(B) 

then  the  N02  group  for  example  will  make  the  base  (as  BX 
may  be  considered)  more  active,  corresponding  to  the 
greater  ionization  constants  of  bases.  It  has  been  observed, 


SOME  CHEMICAL  REACTIONS.  125 

with  reference  to  the  explanation  of  the  mechanism  of  the 
reactions,  that  the  readiness  of  formation  of  addition  com- 
pounds in  general  increases  with  the  strength  of  the  acid 
(cf.  J.  Kendall  and  others). 

The  advantage  of  classifying  reactions  of  organic  chem- 
istry in  the  given  manner  also  becomes  apparent  in  connec- 
tion with  such  reactions  as  the  decomposition  of  ketones  by 
alkalies,  the  "acid"  decomposition  of  acetoacetic  ester,  the 
decomposition  of  acids  into  hydrocarbons  and  carbon 
dioxide,  the  hydrolysis  of  tetranitromethane  to  form  trini- 
tromethane,  etc.  They  may  also  be  classed  together  as  the 
same  type  of  so-called  "double  decomposition"  reaction. 
It  is  also  evident  from  this  point  of  view  that  esters  may  be 
decomposed  with  benzene  in  an  analogous  manner  to  their 
hydrolysis  by  water.  The  relation  between  aldol  condensa- 
tion, esterification,  etherification,  etc.,  is  brought  out. 
Again,  a  point  of  similarity  to  inorganic  reactions  is  the 
effect  of  the  catalyst.  It  is  well  known  that  different  sol- 
vents influence  the  electrolytic  dissociation  of  inorganic 
acids,  for  example,  to  different  extents.  A  similar  phe- 
nomenon is  observable  in  these  double  decomposition 
reactions.  It  is  found,  in  the  type  equation,  that  when  A 
is  aryl  and  B  is  alkyl,  that  aluminium  chloride,  sulfuric 
acid,  and  zinc  chloride  act  as  good  catalysts,  or  in  other 
words,  that  HA  and  BX  are  highly  active,  corresponding 
to  large  ionization  in  inorganic  reactions.  On  the  other 
hand,  if  A  is  aliphatic  in  nature,  it  appears  that  very  often 
alkalies  are  superior  to  acids  as  catalysts,  alkalies,  amines, 
and  alcoholates  being  used,  as  for  example,  in  the  aldol 
condensation.  This  corresponds  to  a  change  in  the  solvent 
with  different  substances  in  order  to  obtain  a  greater 
degree  of  activity  of  the  reacting  substances. 

The  statement  has  already  been  made  in  the  preceding 
pages  that  the  present  definition  for  ionization  is  inadequate. 
At  present  a  compound  in  solution  is  considered  to  be  in 


126  CHEMICAL   REACTIONS. 

the  ionic  condition  when  it  conducts  the  electric  current 
if  placed  between  two  electrodes  of  different  potentials. 
To  emphasize  more  fully  the  probability  that  the  concep- 
tion of  ionization  is  not  altogether  satisfactory,  a  few  re- 
actions may  be  considered  in  more  detail.  The  hydrolysis 
of  an  inorganic  salt  is  explained  by  the  ionic  theory  as 

MeX^  Me+X" 

follows:  HOH^Olf+H1*      ^   H^  *s  a  wea^  ac^  (sngntly 

4t     It 

MeOH  HX 

ionized)  then  the  H+  from  the  H2O  will  remove  the  X~  as 
HX  in  solution,  increasing  the  concentration  of  the  Me+ 
and  OH~~,  and  resulting  in  the  hydrolysis  of  the  salt.  If 
the  MeOH  is  a  weak  base  then  the  OH~  from  the  H2O 
will  remove  Me+  from  solution  and  cause  hydrolysis.  It  is 
assumed  in  each  case  that  the  salt  MeX  is  highly  ionized. 
If  in  the  first  case,  HX  is  insoluble  and  in  the  second 
MeOH  is  insoluble,  hydrolysis  of  the  salt  will  take  place 
as  well.  The  OH~  or  H+  concentrations  may  be  increased 
by  the  addition  of  alkali  or  acid  to  the  solution  of  the  salt. 
A  specific  example  may  be  taken,  namely: 

MgCl2  +  2HOH  =  Mg(OH)2  +  2HC1. 

This  reaction  takes  place  especially  if  KOH  is  used  instead 
of  HOH,  since  the  concentrations  of  the  various  ions  at  the 
equilibrium  condition  of  the  system  are  such  that  the 
solubility  product  of  the  Mg(OH)2  is  exceeded.  If,  how- 
ever, in  place  of  MgCl2,  MgRCl  is  used,  that  is  to  say  the 
Grignard  reagent,  it  will  be  observed  that  this  compound 
is  decomposed  more  rapidly  by  the  HOH  than  is  the  MgCl2. 
This  reaction  is  generally  considered  only  from  the  double 
decomposition  standpoint,  the  resultants  and  reactants,  in 
organic  chemistry,  and  is  not  considered  from  the  ionic 
standpoint.  It  is  impossible  to  state  whether  this  sub- 
stance is  ionized  in  a  water  solution  since  it  is  immediately 


SOME  CHEMICAL  REACTIONS.  127 

decomposed.  But  in  ether  it  does  conduct  the  electric 
current  (J.  M.  Nelson  and  W.  V.  Evans,  Jour.  Amer.  Chem. 
Soc.  39,  82  (1917)),  but  up  to  date  the  nature  of  the  ions  is 
uncertain.  The  reaction  with  water  is  hydrolysis  and  very 
likely  of  similar  character  to  the  decomposition  of  the 
MgCl2.  MgRX  +  2HOH  =  Mg(OH)2  +  RH  +  HX  or 
MgRX  +  HOH  =  MgOHX  +  RH.  With  these  equations 
it  is  still  possible  to  consider  the  same  explanation,  namely 
ionic,  for  the  decomposition  of  the  Grignard  reagent  and 
of  the  magnesium  chloride.  It  is  well  known,  however, 
that  the  Grignard  reagent  is  used  to  a  great  extent  in 
organic  syntheses  in  which  it  is  decomposed  by  oxygen  com- 
pounds other  than  water.  Thus,  aldehydes,  ketones,  carbon 
dioxide,  cyanides,  etc.,  stated  in  organic  chemistry  to  con- 
tain unsaturated  groups,  react  with  the  MgRX.  The 
simplest  way  to  account  for  the  reactions  is  to  compare 
them  with  the  hydrolysis  of  the  RMgX  by  water. 


5--<?- 


,+  0<"  =  MgCT+HR 


o-c=o 

Rl 

This  way  of  indicating  the  changes  makes  it  evident  that 
the  aldehyde  and  the  carbon  dioxide  act  in  the  same  way 
as  the  water,  but  the  aldehyde  and  the  carbon  dioxide 
are  not  considered  as  electrolytes  and  hence  the  ionic 
explanation  seems  to  be  inadequate. 

The  classifications  and  general  relations  developed  here 
together  with  evidence  presented  in  a  paper  published  some 
years  ago  (K.  G.  Falk  and  J.  M.  Nelson,  Jour.  Amer.  Chem. 
Soc.  37,  1732  (1915))  apparently  justify  the  conclusion 
that  the  changes  occurring  in  chemical  reactions  do  not 
depend  upon  the  electrolytic  dissociations  of  the  reacting 
substances.  The  chemical  changes  are  accompanied  very 
often  by  electrolytic  dissociation  phenomena,  but  the  latter 


128  CHEMICAL  REACTIONS. 

parallel  the  former  (or  vice  versa)  and  do  not  necessarily 
precede  or  cause  them.  For  organic  reactions  it  need  not 
be  necessary  to  present  further  evidence  in  this  connection. 
With  inorganic  reactions,  however,  the  question  appears  not 
to  be  so  simple.  The  theory  of  electrolytic  dissociation  does 
not  necessarily  postulate  that  only  ions  react.  For  some  time 
after  the  theory  of  electrolytic  dissociation  was  proposed,  it 
was  attempted  to  apply  the  theory  to  every  possible  case 
where  there  was  the  slightest  possibility  of  an  explanation 
based  upon  it.  In  recent  years  the  trend  of  thought  has  taken 
a  different  turn,  and  the  explanations  of  certain  reactions, 
which  at  one  time  had  been  assumed  to  be  purely  ionic  in 
character,  considered  the  un-ionized  molecules  as  also  taking 
part  in  the  reactions.  The  first  steps  in  this  development 
were  taken  by  G.  Senter  (J.  Chem.  Soc.  91,  467  (1907)) 
and  by  S.  F.  Acree  (Am.  Chem.  J.  37,  410;  38,  258  (1907)), 
and  these  have  since  been  followed  by  S.  Arrhenius,  G. 
Bredig,  H.  C.  S.  Snethlage,  H.  Goldschmidt,  H.  M.  Dawson, 
A.  Lapworth,  H.  S.  Taylor,  J.  Stieglitz,  and  others,  who 
favor  the  view  that  both  ionized  and  un-ionized  molecules 
are  active  in  chemical  changes  even  in  aqueous  solution 
and  present  evidence  bearing  on  the  question. 

According  to  the  views  presented  here,  electrolytic  dis- 
sociation is  not  the  forerunner  of  chemical  reactions  and  in 
fact  chemical  reactions  do  not  depend  upon  the  presence 
of  ions  as  postulated  in  that  theory.  Certain  physical 
properties  of  substances,  which,  early  in  the  history  of 
the  electrolytic  dissociation  theory,  were  considered  to  be 
dependent  upou.  ionization,  have  since  been  shown  to  be 
independent  of  it.  Thus,  the  color  of  a  salt  in  solution 
was  assumed  to  be  made  up  of  the  different  colors  of  the 
ions  and  the  un-ionized  molecule.  Later  work  showed  that 
ionization  changes  do  not  affect  the  color  of  the  substance. 
Reference  may  be  made  here  to  a  detailed  review  of  these 
relations  published  by  J.  Lifschitz  (Sammlung  chemischer 


SOME  CHEMICAL  REACTIONS.  129 

und  chemisch-technischer  Vortrage,  Vol.  21,  Nos.  5-7, 
p.  175  (1914)).  The  explanations  advanced  at  different 
times  with  regard  to  the  color  changes  of  indicators  illus- 
trate these  views  very  well.  Ostwald  in  1894  ("Die  wissen- 
schaftlichen  Grundlagen  der  analytischen  Chemie,"  p.  104) 
attributed  the  different  color  of  an  indicator  in  acid  or 
alkaline  solution  to  the  different  colors  of  the  ions  and  un- 
ionized molecules.  If  the  indicator  substance  itself  was 
an  acid,  the  color  in  acid  solution  would  be  that  of  the 
un-ionized  molecule,  while  in  alkaline  solution  the  color 
would  be  that  of  the  negative  ion.  If  the  indicator  sub- 
stance was  a  base,  the  color  in  alkaline  solution  would  be 
that  of  the  un-ionized  molecule,  in  acid  solution  that  of  the 
positive  ion.  This  theory  was  shown  not  to  be  general 
enough  to  include  the  observed  phenomena,  and  was  re- 
placed by  the  "chemical"  theory  first  suggested  (for  phenol- 
phthalein)  by  Bernthsen  and  developed  by  J.  Stieglitz 
(Jour.  Am.  Chem.  Soc.  25,  1112  (1903))  and  especially  by 
A.  Hantzsch  Ber.  39,  1090  (1906)  and  numerous  articles 
since)  who  showed  the  ionic  theory  of  indicators  to  be 
highly  improbable.  The  present  view  considers  every 
change  in  color  of  an  organic  substance  to  be  due  to  an 
intramolecular  rearrangement.  Indicators  form  a  special 
group  in  so  far  as  the  intramolecular  rearrangements  in 
their  case  are  tautomeric  in  character  and  include,  therefore, 
in  most  cases  the  shifting  of  a  hydrogen  atom  in  passing 
from  one  form  to  the  other.  The  production  of  ions  is 
secondary  in  the  tautomeric  changes,  and  if  the  ions  are 
colored,  it  is  because  the  un-ionized  molecules  from  which 
they  are  derived  are  colored.  The  equilibrium  between  the 
tautomeric  forms  of  a  substance  depends  upon  a  variety 
of  factors,  such  as  solvent,  temperature,  small  amounts  of 
certain  added  substances  such  as  acids  or  bases,  etc. 
Hantzsch  has  shown  the  important  part  played  by  solvents 
in  affecting  the  equilibrium  (and  therefore  the  color  change) 


130  CHEMICAL  REACTIONS. 

between  the  tautomeric  forms  of  some  indicators  (Ber.  4$> 
158  (1915)).  Such  actions  take  place  with  indicators  in 
solution  in  practical  titrations  where  the  indicator  substance 
is  present  in  such  small  concentration  that  the  color  change 
which  accompanies  the  transformation  of  one  tautomer  into 
the  other  is  very  marked  with  the  relatively  small  amount 
of  added  substance  necessary  to  produce  it  (cf .  A.  A.  Noyes, 
Jour.  Amer.  Chem.  Soc.  88,  815  (1910)).  Other  changes  of 
conditions  may  be  considered  similarly  for  the  indicators  as 
a  special  class  of  tautomeric  substances.  In  general,  it 
may  be  stated  that  the  various  factors  which  influence  the 
equilibrium  between  tautomers  also  influence  the  equi- 
librium between  the  different  tautomeric  forms  of  indicators, 
and  that  the  question  of  the  electrolytic  dissociation  of  the 
indicator  substances  does  not  enter  into  the  theory  of  their 
color  changes  as  assumed  in  the  earlier  theory,  although  it 
appears  to  be  connected  with  one  of  the  factors  involving 
the  sensitiveness. 

It  is  evidently  possible  to  extend  this  method  of  treatment 
to  other  reactions.  No  more  will  be  taken  up  at  present, 
but  the  view  will  be  emphasized  that  chemical  reactions 
need  not  be  considered  to  depend  upon  electrolytic  dissocia- 
tion. With  the  atoms  in  a  molecule  all  carrying  electric 
charges,  certain  properties  of  a  solvent  make  some  of  these 
charges  evident  to  experimental  methods,  while  certain, 
perhaps  very  often  the  same,  properties  of  the  solvent 
increase  the  extent  or  rate  of  a  reaction.  These  phenomena 
are  independent  of  each  other  but  both  dependent  upon  the 
solvent,  or  possibly  some  other  underlying  cause.  Many,  if 
not  all,  of  the  changes  which  have  been  considered  hereto- 
fore as  metatheses,  involve,  without  doubt,  primary  addition 
and  subsequent  decomposition  or  splitting  off  in  various 
ways  of  the  reacting  molecules. 

The  question  of  tautomerism  and  the  factors  influencing 
it  may  be  considered  further  in  the  same  way  as  organic 


SOME  CHEMICAL  REACTIONS.  131 

reactions  in  general.  To  illustrate:  In  the  general  type 
reaction  BX  +  HA  =  HX  +  BA,  if  instead  of  considering 
both  molecules  to  be  separate  entities,  they  are  considered 
to  be  components  of  a  single  more  complex  molecule,  then 
the  change  would  be  a  case  of  tautomerism.  The  following 
examples  will  show  this: 

X      B  +  A    H          HX-t-B     _±_ 
O  =  N-]SKH    =   HO    N='N    Otf 
OH 


BX+H     A  B  X  H 


A 


Since  A  is  an  aliphatic  "negative"  group  in  the  second 
example,  the  compound  is  more  "active"  and  shows  tauto- 
merism more  readily.  The  factors  which  influence  the 
activity  of  organic  compounds  as  pointed  out  before  in- 
fluence the  activity  of  these  compounds  enabling  them  to 
show  the  tautomerism  or  to  exist  more  readily  in  mutually 
convertible  forms.  Tautomeric  changes  may  therefore  be 
included  in  this  group  of  organic  reactions  and  the  same 
laws  and  relations  apply  to  all. 

The  classifications  and  explanations  of  the  mechanisms 
of  reactions  which  have  been  developed  have  been  illus- 
trated by  means  of  qualitative  examples.  Innumerable 
examples  of  the  reactions  might  be  cited  but  unfortunately 
the  quantitative  data  at  hand  are  too  few  to  permit  of 
general  conclusions.  The  possibilities  in  the  way  of  dif- 
ferent products  being  formed  also  complicate  the  quantita- 
tive study  with  many  organic  reactions. 

A  beginning  has  been  made  in  the  problem  of  obtaining 
quantitative  measures  of  relative  stability  for  a  number  of 
organic  compounds.  Reference  may  be  made  to  several 
papers  by  C.  G.  Derick  bearing  on  this  question  (Jour. 
Amer.  Chem.  Soc.  32,  1333  (1910);  S3,  1152  (1911)). 


132  CHEMICAL  REACTIONS. 

Some  of  his  conclusions  from  his  experimental  work  may  be 
given : 

In  his  first  paper  he  takes  up  the  question  of  stability  of 
isomeric  compounds  which  rearrange  to  form  more  stable 
substances  to  a  practically  irreversible  extent  under  the 
given  conditions.  Quantitative  data  are  supplied  for  a 
series  of  such  changes.  The  rearrangement  of  a  number 
of  acids  and  bases  to  more  stable  configurations  was  given. 
The  stability  of  these  compounds  toward  ionization  was 
used  as  a  measure.  The  equation  A  =  RT  logc  K  was 
made  use  of,  A  representing  the  free  energy  of  ionization; 
R,  the  gas  constant;  T,  the  absolute  temperature;  and  K, 
the  ionization  constant.  The  free  energy  of  ionization  of 
acids  and  of  bases  is  shown  as  the  change  in  free  energy  of  the 
reactions  HA  ^  H+  +  A~  for  acids  and  ROH  ^  R+  +  OH~ 
for  bases  (omitting  the  part  played  by  the  solvent),  when 
the  initial  and  final  substances  are  at  unit  concentration.  It 
is  evident,  therefore,  that  the  free  energy  of  ionization  is 
directly  proportional  to  the  natural  logarithm  of  the  ioniza- 
tion constant,  and  that  to  determine  the  relative  stabilities 
of  two  acids  (or  bases)  in  terms  of  the  free  energy  of  ioniza- 
tion, it  is  only  necessary  to  compare  the  logarithms  of  their 
ionization  constants.  Since  an  acid  is  more  stable  toward 
ionization  when  it  possesses  a  smaller  ionization  constant 
or  smaller  free  energy  of  ionization,  the  stability  toward 
ionization  of  an  acid  is  greater  the  smaller  its  ionization 
constant.  The  exact  measures  of  stability  are  given  by  the 
logarithms  of  these  ionization  constants.  Derick  gives  the 
results  of  a  number  of  isomeric  organic  acids,  and  draws 
some  general  conclusions  with  regard  to  their  structures 
and  relative  stabilities  toward  ionization.  For  example,  for 
tetrahydrobenzenecarboxylic  acids,  he  finds  that  "  whenever 
the  unsaturation  is  A2  with  respect  to  a  given  carboxyl 
group  true  rearrangements  of  the  non-reversible  type  are 
possible"  and  also  "the  compounds  from  which  Thiele 


SOME  CHEMICAL  REACTIONS.  133 

deduced  his  theory  of  partial  valence,  as  well  as  other  acids 
which  obey  the  same  rule,  must  be  compounds  which  are 
formed  with  weak  reducing  agents  involving  small  energy 
changes  and  where  the  speed  of  reaction  is  small  so  that 
compounds  result  which  are  very  unstable  toward  ioniza- 
tion,  and  therefore  toward  rearrangement."  In  addition  to 
these  quantitative  results,  a  number  of  rearrangements  are 
grouped  in  Derick's  first  paper  under  various  headings. 
These  relations  are,  however,  only  qualitative  in  character. 
In  a  second  series  of  papers,  Derick  goes  farther  and 
studies  the  "polarity  of  elements  and  radicals  measured  in 
terms  of  a  logarithmic  function  of  the  ionization  constant." 
This  is  evidently  the  direction  in  which  advance  is  to  be 
expected,  a  study  of  the  action  of  various  groups  on  the 
equilibria  of  certain  reactions  in  terms  of  affinity  changes. 
The  following  definitions  are  given  by  Derick: 

1.  An  element  or  radical  possesses  positivity  if,  when  it  is 
substituted  for  a  hydrogen  of  water,  it  increases  the  hy- 
droxyl  ionization.     It  is  therefore  said  to  be  positive. 

2.  An  element  or  radical  possesses  negativity  if,  when  it 
is  substituted  for  a  hydrogen  of  water,  it  increases  the 
hydrogen  ionization.     It  is  therefore  said  to  be  negative. 

Water  is  used  as  the  standard  for  determining  the  polarity 
of  various  groups.  The  relative  free  energies  toward 
ionization  of  the  various  substances  are  used  to  determine 
the  relative  stabilities,  and  in  this  sense  the  classification  is 
limited.  It  is  however  useful  and  important  as  a  com- 
parison of  the  stabilities  toward  a  certain  transformation 
and  giving  a  measure  of  the  effect  on  a  definite  reaction  of 
different  groups.  A  table  is  given  of  a  number  of  these 
ionization  constants  (Ka  and  K&  for  acidic  and  basic  ioniza- 
tion) and  the  free  energy  values  (RT  logc  K) .  In  the 
succeeding  papers  (and  also  later  (with  O.  Kamm)  in  the 
Jour.  Amer.  Chem.  Soc.  39,  388  (1917))  Derick  takes  up  a 
number  of  reactions  and  discusses  the  effects  of  various 


134  CHEMICAL  REACTIONS. 

groups  upon  the  stabilities  of  the  reactions.  No  attempt 
will  be  made  to  discuss  in  detail  the  applications  and  con- 
clusions of  Derick  here,  but  the  reader  is  referred  to  his 
papers  for  a  careful  study  of  the  work.  This  is  perhaps  the 
first  systematic  attempt  to  study  in  a  quantitative  way 
the  affinity  relationships  of  a  large  number  of  organic  com- 
pounds, and  to  obtain  exact  data  with  regard  to  the  effects 
of  different  groups  on  the  equilibrium  constants  and  there- 
fore the  stabilities  in  certain  reactions  in  various  molecules. 
The  importance  of  this  work  must  therefore  be  emphasized 
as  marking  a  beginning  of  the  systematic  quantitative  study 
of  reactions  such  as  have  been  given  in  these  chapters, 
where  for  lack  of  sufficient  data,  only  the  qualitative  aspects 
could  be  presented. 


CHAPTER  VIII. 

OLEFINS  AND  THEIR  REACTION  PRODUCTS. 

IT  was  stated  in  the  preceding  chapters  that  the  reactions 
of  organic  chemistry  may  be  treated  from  the  same  point 
of  view  as  the  reactions  which  have  been  classed  under 
inorganic  chemistry.  The  same  general  relations  apply 
to  all  reactions  in  chemistry,  even  if,  because  of  convenience 
in  grouping  or  presentation,  they  have  been  classed  sepa- 
rately. A  certain  justification  for  the  separate  treatments 
is  found  in  the  fact  that  characteristic  phenomena  are  pre- 
dominant in  some  reactions  which  are  more  in  the  back- 
ground in  other  reactions.  Even  if  this  is  true,  it  must 
be  remembered  that  the  same  underlying  principles  apply 
to  all  reactions  and  that  the  laws  or  generalizations  of 
chemistry  must  necessarily  hold  for  all  chemical  phenomena, 
and  not  one  set  of  laws  for  some  compounds  and  another 
set  for  other  compounds.  At  most,  no  sharp  dividing  line 
is  ever  supposed  to  exist  between  the  two,  but  only  a 
gradual  transition  set  of  compounds  or  reactions,  which 
may  belong  to  one  group  or  to  the  other.  The  point  of 
view  to  be  emphasized  is  again  similar  to  the  point  of  view 
presented  in  Chapter  I,  in  which  it  was  shown  that  two 
kinds  of  valence,  polar  and  non-polar,  were  unnecessary  in 
the  development  of  atomic  valence  structures. 

In  taking  up  some  of  the  reactions  of  organic  chemistry, 
the  group  of  compounds  which  come  to  mind  as  being  very 
reactive,  reactive  in  the  sense  of  reacting  rapidly  with  a 
large  number  of  different  reagents,  is  the  olefins.  This 
property  of  reacting  with  many  compounds  is  well  brought 
out  for  these  compounds  in  the  term  "unsaturated  hydro- 
carbons." The  use  of  the  term  "unsaturated"  was  applied 
in  Chapter  V  to  other  compounds  which  formed  addition 
10  135 


136  CHEMICAL  REACTIONS. 

compounds  also.  Ammonia  was  used  there  as  a  typical 
example.  Because  of  the  general  point  of  view  which  is 
emphasized  here,  the  comparative  study  of  the  unsaturated 
properties  of  the  olefins  and  of  ammonia  will  be  of  value. 

The  combination  of  olefins  with  acids  to  form  esters,  etc., 
is  strikingly  similar  to  the  combination  of  ammonia  and 
acids  to  form  salts.  In  the  great  majority  of  these  com- 
pounds one  molecule  of  the  olefin  or  ammonia  combines 
with  one  equivalent  of  the  acid.  The  reaction  is  also 
reversible  in  both  series.  Designating  the  olefin  by  the 
symbol  En,  (ethylene  as  example),  the  following  reactions 
may  be  given. 

En  +  HC1  =  EtCl  (Et  denoting  Ethyl), 

En  +  H2O  =  EtOH  (Water  taking  the  part  of 

the  acid), 

CsHio  +  H02C.CC13  =  CsHiACCClg, 
En  +  H2SO4  =  EtHSO4, 

CHsCftEt  =  En  +  CH3C02H 

(A.  Oppenheim  and  H.  Precht,  Ber.  9,  325,  (1876). 

Esters  may  be  regarded  as  the  olefinates  of  acids,  just  as 
ammonium  salts  can  be  looked  upon  as  the  ammoniates  of 
acids.  Just  as  ammonia  combines  with  salts  such  as  PtCLi, 
CaCl2,  etc.,  to  form  ammoniates,  so  may  olefins  combine 
with  salts  to  form  olefinates.  Compounds  of  this  last 
type  have  not  been  studied  extensively,  but  the  following 
may  be  mentioned:  (CH3)2C  :  CHCH3.2ZnCl2  (from  iso- 
butylene  and  zinc  chloride)  [J.  Kondakow,  J.  pr.  Chem. 
(2)  48,  474  (1893)];  C2H4.PtCl4  [V.  Meyer  and  P.  Jacobson, 
Lehrbuch  der  organischen  Chemie,  Vol.  1,  p.  832  (1907)]; 
etc. 

So-called  "anomalous"  olefinates,  which  contain  a  dif- 
ferent proportion  of  acid  or  salt  than  the  1  :  1  ratio  are  also 
known.  The  zinc  chloride  compound  just  given  is  an 
example;  partially  saturated  polyolefins,  such  as  the  mono- 


OLEFINS  AND  THEIR  REACTION  PRODUCTS.      137 

halogen  addition  products  of  terpenes  as  menthadienes, 
belong  to  this  group;  ethyl  ether  may  be  looked  upon  as  a 
diolefinate  of  water;  the  compound  (CH3)2O.C2H4  [G. 
Baume  and  A.  F.  O.  Germann,  C.r.  153,  569  (1911)]  may 
be  written  (CH2)4.H2O;  C2H4.7H20  [R.  de  Forcrand,  C.r. 
135,  959  (1902)]  is  an  example;  a  complex  alkyl  halide 
CH3  /H 

c — c 


such 


CHo  Cl 


as 


\ 


CH 


3  may  be  formed  by  the  combin- 


CTT  \  /^TT 

2il5  CH3 

ation  of  several  molecules  of  simpler  olefins  and  one  mole- 
cule of  hydrogen  chloride  (Meyer  and  Jacobson,  pp.  833, 
836);  etc. 

Mixed  addition  compounds  containing  olefins  have  also 
been  described;  for  example,  FeCl2.C2H4.H2O  [J.  Kachler, 
Ber.  2,  510  (1869)];  FeBr2.C2H4.H2O  [C.  Chojnacki,  Z.f. 
Chem.  1870  p.  419)];  (CH3)2O.NH3,  an  olefinate  and  am- 
moniate  of  water,  etc. 

These  reactions  show  the  similarity  between  the  olefins 
and  ammonia,  and  that  the  common  property  of  unsatura- 
tion  in  both  leads  to  the  formation  of  analogous  products. 

The  simplest  compounds  which  are  formed  from  the 
olefins  are  the  alkyl  halides,  which  correspond  to  the 
ammonium  halides.  There  is  at  present  no  direct  experi- 
mental evidence  of  the  action  of  catalysts  in  their  formation, 
but  in  their  dissociation  into  olefin  and  hydrogen  halide, 
aluminium  chloride,  zinc  chloride,  etc.,  affect  the  rate  of 
reaction  greatly  [P.  Sabatier  and  A.  Maihle,  C.r.  138,  407 
(1904);  141,  238  (1905)].  This  shows  itself  more  particu- 
larly in  the  lower  temperature  necessary  for  their  rapid 
dissociation.  The  alkyl  chlorides  dissociate  more  readily 
than  do  the  bromides,  and  these  more  readily  than  do  the 
iodides.  Although  no  exact  quantitative  data  regarding  the 


138  CHEMICAL  REACTIONS. 

velocities  and  equilibria  of  these  reactions  are  at  hand,  they 
may  be  considered  to  be  analogous  to  the  relative  degrees  of 
dissociation  of  the  ammonium  halides  studied  by  A.  Smith 
and  co-workers  [Jour.  Amer.  Chem.  Soc.  87,  38  (1915)]. 
The  action  of  certain  substances  such  as  alkalis  in  these 
reactions  will  be  taken  up  later  in  this  chapter. 

A  further  relation  of  the  alkyl  halides  may  be  mentioned. 
Under  the  same  conditions,  the  primary  halides  dissociate 
more  readily  than  the  secondary,  and  the  secondary  more 
readily  than  the  tertiary  (Sabatier  and  Maihle,  I.e.).  In 
the  study  of  this  reaction,  no  statement  was  made  as  to  the 
probable  equilibria.  [It  will  have  been  noticed  that  in  the 
discussion  of  organic  reactions,  the  experiments  often  are 
not  definite  or  quantitative.  This  leads  to  uncertainty  in 
the  theoretical  treatment,  as  to  whether  a  ready  formation 
of  a  compound  refers  to  the  velocity  under  certain  conditions 
or  to  the  amount  present  under  equilibrium  conditions. 
Careful  regulation  of  conditions  and  quantitative  working 
are  essential  for  the  further  development  of  the  science  of 
reactions  included  in  organic  chemistry.]  It  is  possible  to 
conceive  of  the  tendency  of  the  n-alkyl  halides  going  over 
into  the  iso  on  boiling,  or  of  the  formation  of  isopropyl 
benzene  from  n-propyl  chloride  and  benzene  by  the  Friedel- 
Crafts  reaction,  as  due  to  the  different  equilibria  of  the 
olefin  and  hydrogen  halide  with  different  sets  of  products 
(normal)  iso,  and  tertiary  halides);  the  one  which  is  found 
experimentally  depending  upon  the  conditions  of  the  various 
equilibria,  or  the  relative  velocities  of  the  reactions. 
Connected  with  this  is  the  reaction  in  which  hydrogen 
halide  is  added  to  an  olefin,  the  halogen  being  finally  com- 
bined mainly  with  the  carbon  with  least  hydrogen;  that  is  to 
say,  to  form  the  tertiary  compound  preferably,  secondarily 
the  iso-compound  [A.  Michael  Ber.  89,  2138  (1906)].  An- 
other example  of  the  same  kind  is  the  formation  of  2-brom-, 
2,  2,  1,  trimethyl  ethane  by  heating  1-brom-,  2,  2,  2- 
trimethylethane 


OLEFINS  AND  THEIR_  REACTION  PRODUCTS.      139 
CH3  ,CH3        CH3        CH3  C^s         /CH3 


_ 

H  —  C  —  Br  H          H  /  \ 

I  H  H 

H 

[L.  Tissier,  Ann.  de  chim.  et  de  phys.  (6)  29,  359,  361,  364 
(1893)]. 

A  general  method,  used  very  often  practically,  for  the 
preparation  of  olefins  consists  in  the  action  of  an  alcoholic 
solution  of  potassium  hydroxide  on  an  alkyl  halide.  This 
reaction  is  analogous  to  the  production  of  ammonia  from 
ammonium  chloride  and  an  aqueous  solution  of  an  alkali. 
The  equations  for  the  latter  are  generally  given  as  the 
following  : 

NH4C1          =  NH4+  +  Cl,  (1) 

KOH  =  K+  +  OH,  (2) 

NH4+  +  OH  =  NH4OH,  (3) 

NH4OH       =  NH3  +  H20.  (4) 

Omitting  the  action  of  water  in  these  equations,  (1)  and 
(2)  represent  the  ionization  in  solution.  Equation  (3) 

•f  _ 

shows  the  equilibrium  between  NH4  and  OH  ions  and 
un-ionized  NH4OH.  Equation  (4)  shows  the  equilibrium 
between  the  last  named  substance  and  its  dissociation 
products,  ammonia  and  water.  Since  the  last  reaction 
takes  place  to  a  great  extent  to  form  the  products  of  dis- 
sociation, there  will  be  a  progressive  action  to  form  am- 
monia, especially  if  it  is  removed  from  the  sphere  of  action 
by  heat  or  in  some  other  way,  or  if  the  concentration  of  OH 
is  very  large,  until,  finally,  all  the  ammonium  chloride  has 
reacted  to  form  ammonia.  If  the  same  explanation  were 
applicable  to  the  alkyl  halide,  the  following  equations 
would  hold: 


140  CHEMICAL  REACTIONS. 

C2H5C1  =  C2H5+  +  Cl, 

KOH  =  K  +  OH, 

C2H5+  +  OH  =  C2H5OH, 
C2H5OH         =  C2H4  +  H20. 

This  explanation  is  not  satisfactory  for  olefins.  In  the 
first  place,  no  evidence  is  at  hand  indicating  that  the  alkyl 
halides  ionize.  One  of  the  arguments  advanced  to  meet 
this  criticism  is  that  the  solvent  in  the  case  of  the  formation 
of  the  olefin  is  not  water  and  therefore  the  two  cases  are 
not  comparable.  If  water  were  used  as  the  solvent,  the 
solubility  of  the  alkyl  halide  would  be  so  small  that  ioniza- 
tion  in  solution  could  not  be  detected  by  any  of  the  present 
methods.  On  the  other  hand,  very  small  concentrations  of 
ions  can  be  detected  experimentally.  Most  chemists,  there- 
fore, do  not  attempt  to  explain  the  reactions  of  alkyl  halides 
on  the  ionization  basis.  The  two  reactions,  the  formation 
of  ammonia  and  the  formation  of  olefins,  consequently  are 
considered  to  be  quite  different. 

If  the  formation  of  ammonia  from  ammonium  salts  is 
considered  from  the  addition-dissociation  and  displacement 
point  of  view,  the  two  reactions  become  analogous.  Upon 
this  basis  the  formation  of  ammonia  may  be  indicated  as 
follows : 

f  HCl          Solution  of  the  ammonium 
NH4C1  +  nH20  =      NH3      chloride.     (NI^Cl  might  be 
L(H2O)nJ  written  for  NH3,  HCl.) 

HCl 
NH3 

(H20)n+m 
KOH 

TKCl  fNH3 


OLEFINS  AND  THEIR  REACTION  PRODUCTS.      141 

Or  it  may  be  represented  according  to  the  general  type 
reaction  (chapter  5)  as  follows: 

[(HaOkNUCl]  +  KOH  =  [(H20)*NH4KOH]C1 

=  NH3  +  (HaO)x+i  +  KC1. 

Similarly  for  the  alkyl  halides;    in  aqueous  solution  the 
equations  would  be: 

[(H20)1/C2H5C1]  +  KOH  =  [(H20)yC2H5KOH]Cl 

=  C2H4+(H20)J/+1+KC1 
and  in  alcoholic  solution: 

[(C2H5OH)ZC2H5C1]  +  KOH  =  [(C2H5OH)2C2H5KOH]C1 

+  (C2H5OH)2  +  H2O  +  KC1. 


It  is  true  that  this  explanation  appears  to  be  more  com- 
plicated than  the  ionic  explanation,  but  it  has  in  its  favor 
the  fact  that  it  is  more  general,  and  unquestionably  repre- 
sents more  nearly  the  mechanism  involved. 

For  most  purposes  it  is  not  necessary  to  write  the  reactions 
in  such  a  complicated  way,  the  following  being  sufficient: 


KOH  +  C2H6C1  = 


KOH  +  NH4C1  = 


KOH 

HC1 

C2H4 

KOH 

HC1 

NH3 


=  KC1  +  C2H4  +  H20, 


=  KC1  +  NH3  +  H2O. 


When  potassium  hydroxide  is  dissolved  in  alcohol,  there 
is  likely  to  be  some  potassium  ethoxide,  KOC2H5,  formed. 
(It  is  incorrect  to  name  compounds  of  this  type  alcoholates, 
since  alcoholates  correspond  to  hydrates,  while  these  com- 
pounds correspond  to  hydroxides.)  There  is,  therefore,  a 
possibility  of  the  formation  of  ethers  when  alkyl  halides 
are  treated  with  an  alcoholic  solution  of  potassium  hydrox- 
ide. 


142  CHEMICAL  REACTIONS. 

KOC2H5 

I  Vv2-tA4  I     /  f~\   TT  /"vTT\       I       ~\7~ f^~\      I       C*   TT 

-rj/^i  —     I  TT  f\    I    W^*  v^2il5^-tly   ~T   J^V_'i  -j-   L/2A14 

±1C1  L^2VJ  J 

^  (or  (C2H5)2O)  +  KC1,  etc. 


Another  very  interesting  point  in  connection  with  the 
reactions  of  the  alkyl  chlorides,  bromides  and  iodides,  is  the 
fact  that  the  iodides  show  a  tendency  to  give  a  larger  yield 
of  olefin  than  do  the  chlorides  in  the  presence  of  alkali 
[A.  Lieben  and  A.  Rossi,  Lieb.  Ann.  158,  164  (1871)]. 
This  is  the  opposite  to  what  would  have  been  supposed 
from  the  behavior  of  the  halides  in  the  presence  of  catalysts 
such  as  aluminium  chloride.  Furthermore,  the  chlorides 
yield  ether  more  readily  than  do  the  corresponding  bromides 
or  iodides  [M.  Wildermann,  Z.  phys.  Chem.  8,  661  (1891); 
and  S.  Brussow,  Ibid.  34,  129  (1900)]. 

All  of  these  reactions  depend  very  likely  upon  the  relative 
velocities  of  the  various  possible  dissociations  of  the  inter- 
mediate addition  compounds  under  the  given  conditions. 

The  reason  why  ordinarily  mixed  ethers  of  the  type 
C2H50NH4  are  not  obtained  is  that  they  undergo  dissocia- 
tion at  such  low  temperatures.  If  the  alcohol-ammonia 
mixture  is  cooled  sufficiently,  these  compounds  are  formed, 
and  may  be  isolated.  For  example,  CH3OH.NH3  and 
(CHs^O.NHs  (G.  Baume  and  co-workers,  J.  de  Chim. 
Phys.  12,  216,  225  (1914))  belong  to  this  type. 

'A  reaction  similar  to  that  of  ammonia  and  of  the  amines 
is  that  by  which  olefins  may  be  alkylated  to  form  olefins 
containing  a  greater  number  of  carbon  atoms.  Thus, 
amylene  treated  with  methyl  iodide  yields  hexylene  and 
heptylene  [(M.  Eltekoff,  Ber.  11, 412  (1878);  J.  Lermontoff, 
Lieb.  Ann.  196,  116  (1879)]. 

C5H10  +  CH3I  =  C6H12  +  HI, 
C6Hio  +  2CH3I  =  C7H14  +  2HI. 


OLEFINS  AND  THEIR  REACTION  PRODUCTS.      143 

The  alcohols  may  be  regarded  as  a  group  of  compounds 
similar  to  the  alkyl  halides  in  being  olefinates  of  water  in 
place  of  acid,  just  as  ammonium  hydroxide  is  an  ammoniate 
of  water.  The  formation  of  an  alkyl  halide  from  an  alcohol 
may  therefore  be  looked  upon  as  the  displacement  of  water 
by  hydrogen  halide. 

[C2H4.H20]  +  HC1  =  [C2H4.HC1]  +  H2O, 
[NH3.H2O]  +  HC1  =  [NH3.HC1]  +  H2O. 

The  olefinates  of  water  differ  from  those  of  the  hydrogen 
halides  in  that  the  tertiary  alcohols  appear  to  lose  water  to 
form  the  olefins  more  readily  than  do  the  secondary,  and 
the  secondary  more  readily  than  do  the  primary.  This  is 
the  opposite  to  the  order  observed  with  the  halides,  but 
whether  this  difference  refers  to  the  actual  thermodynamic 
stability  or  to  the  relative  velocities  under  certain  conditions 
is  not  definite. 

The  formation  of  olefins  from  alcohols  is  similar  to  the 
formation  of  ammonia  from  ammonium  hydroxide : 

[C2H4.H2O]  =  C2H4  +  H20, 
[NH3.H2O]  =  NH3  +  H2O. 

The  olefin  formation  is  influenced  very  much  by  the 
presence  of  other  substances  which  act  as  catalysts.  Sul- 
furic  acid  is  one  of  those  most  commonly  used  in  this 
reaction.  The  efficiency  of  the  sulfuric  acid  in  this  reaction 
is  often  connected  with  its  tendency  to  combine  with  water, 
or  its  dehydrating  property.  In  the  final  products,  it  is 
true  that  the  elements  of  water  have  been  removed  from 
the  alcohol,  but  the  mechanism  of  the  reaction  is  un- 
questionably not  so  simple.  The  continuous  formation 
of  ethylene  by  running  ethyl  alcohol  into  warm  sulfuric 
acid;  the  formation  of  alcohol  from  an  olefin  and  dilute 
sulfuric  acid  [A.  Butleroff,  Lieb.  Ann.  180,  245  (1876)]; 
the  formation  of  alcohol  from  olefin  and  concentrated  sulfuric 


144  CHEMICAL  REACTIONS. 

acid  as  well  as  the  saponification  of  the  ester  formed; — 
all  speak  against  such  a  simple  interpretation.  Since  ethyl 
alcohol  and  sulfuric  acid,  or  olefin  and  sulfuric  acid,  form 
ethyl  sulfuric  acid,  Et  HSO4,  which  breaks  down,  on  heating, 
into  olefin  and  the  acid,  most  textbooks  state  that  the  first 
step  in  this  reaction  is  the  formation  of  this  ester.  Accord- 
ing to  the  general  theory  of  addition  reactions  advanced  in 
this  book,  the  intermediate  compound  would  be  more  com- 
plex, and  the  ethyl  sulfuric  acid  itself  would  be  one  of  the 
products  of  the  dissociation.  A  number  of  equilibria  may 
be  given  to  represent  the  possible  dissociation  products. 
This  list  is  not  complete  but  will  indicate  the  possibilities 
of  the  reaction. 


(H20)b 
H2S04 


EtOH  +  H2S04  +   (b 

n  H2SO4  +  b  H2O  +  (a-l)En  (2) 

.En  +  H2S04  (H20)b  (3) 

En  +  bH2O  +  H2SO4  (4) 

a3    H20  +    H2S04  +  (b^|)  H20  (5) 

En2.  +   (a-2)  En  +   H2S04  +   bH20  (6) 


Equilibrium  (1)  represents  the  reaction  between  ethyl 
alcohol,  sulfuric  acid  and  water  to  form  the  intermediate 
product;  (2)  the  formation  of  the  ethyl  sulfuric  acid;  (3) 
the  formation  of  ethylene;  (4)  the  formation  of  ethylene 
and  the  simultaneous  giving  off  of  water;  (5)  the  formation 
of  ethyl  ether;  (6)  the  formation  of  a  polymer  of  ethylene. 
All  of  these  reactions  have  been  observed  experimentally, 
and  the  products  actually  obtained  under  given  conditions, 
depend  upon  these  conditions  and  the  principles  of  the 
law  of  mass  action.  This  list  served  to  indicate  the  possi- 
bilities for  the  quantitative  study  of  a  common  reaction 
presumably  well-known. 

If  a  different  catalyst  were  used  in  the  above  reaction, 
while  the  various  equilibria  would  be  identical  in  principle, 
the  products  actually  obtained  under  any  set  of  definite 


OLEFINS  AND  THEIR  REACTION  PRODUCTS.      145 

conditions  might  be  different  due  to  the  specific  action  of 
the  catalyst  on  the  different  equilibria.  The  action  of  zinc 
chloride  may  be  cited.  With  trimethyl  ethylene,  the  com- 
pound (CH3)2C  :  CH  CH3.2ZnCl2  has  been  isolated.  With 
water  it  gives  dimethylethyl  carbinol,  (CHa^.C.CH^.CHs; 

OH 

with  hydrogen  chloride,  tertiary  amyl  chloride;  if  heated 
alone,  diisoamylene  [J.  Kondakow,  J.  pr.  Chem.  (2)  4$> 
475  (1893)].  Sulfuric  acid  and  isoamylene  under  suitable 
conditions  yield  diisoamylene  also.  This  polymerization 
reaction  is  used  commercially  in  the  formation  of  synthetic 
rubber  from  the  octadiens.  The  specific  action  of  the 
particular  catalyst  employed  is  shown  also  by  the  fact  that 
iso-propyl  bromide  dissociated  at  the  temperature  of  boiling 
amylene  in  the  presence  of  asbestos,  while  the  n-bromide 
did  not.  [D.  Konowalow,  Ber.  18,  2808  (1885).] 

Although  liquid  ammonia  is  an  associated  liquid  [E.  C. 
Franklin  and  C.  A.  Kraus,  Amer.  Chem.  J.  21,  14  (1899)] 
similar  polymerization  reactions  have  not  been  observed 
with  ammonia  or  amines. 

The  acetylene  hydrocarbons  may  be  studied  from  the 
same  point  of  view  as  the  olefin  hydrocarbon.  They  only 
differ  in  the  degree  and  amount  of  unsaturation. 

It  was  shown  that  alkyl  halides  may  be  formed  from 
olefins  and  acids  and  may  be  looked  upon  as  salts  of  the 
hydrogen  halides,  or,  as  organic  chemists  have  been  in 
the  habit  of  calling  such  salts,  as  esters  of  the  halogen  acids. 
In  speaking  of  the  alkylation  of  olefins,  it  was  pointed  out 
that  alkyl  halides  add  to  olefins,  the  alkyl  radical  playing 
the  same  part  as  the  hydrogen  of  the  hydrogen  halide  in 
such  reactions.  Zinc  chloride  facilitated  the  addition  of 
the  alkyl  halide  to  the  olefin  as  J.  Kondakow  [J.  pr.  Chem. 
54,  452  (1896)]  showed.  He  described  the  reaction  as 
follows: 


146  CHEMICAL  REACTIONS. 

(CH3)2C  :  CH  CH3  +  C1.C(CH3)2(C2H6)  +  ZnCh 

=  (CH3)2C-CHCHs 

Cl     C(CH3)2C2H6 
+  ZnCl2. 

As  he  did  not  examine  the  intermediate  addition  com- 
pound of  the  three  reacting  components,  but  treated  the 
mixture  directly  with  water,  removing  the  zinc  chloride, 
he  could  not  determine  the  action  of  the  latter.  He  did 
notice,  however,  that  when  the  olefin-zinc  chloride  addition 
compound  was  treated  with  hydrogen  halide,  the  latter 
replaced  the  zinc  chloride  and  formed  the  corresponding 
alkyl  halide  [J.  pr.  Chem.  48,  475  (1893)].  At  higher  tem- 
peratures, large  amounts  of  the  polymerized  olefin  were 
formed.  These  various  reactions  can  be  accounted  for 
on  the  basis  of  various  equilibrium  equations. 

Many  other  salts  have  properties  similar  to  those  of  zinc 
chloride.  Thus,  G.  Gustavson  [J.  pr.  Chem.  (2)  34,  161 
(1886)]  found  that  aluminium  bromide  formed  a  compound 
with  butylene,  and  the  use  of  mercury  salts  for  the  hydra- 
tion  of  olefins  and  acetylenes,  etc.,  may  be  quoted.  For  the 
further  discussion  of  the  addition  of  alkyl  halides  to  olefins, 
the  reader  is  referred  to  the  chapter  on  the  Friedel-Crafts 
reaction.  Just  as  amines  and  ammonia  react  with  acid 
anhydrides  and  acid  chlorides,  so  do  the  olefins.  J.  Konda- 
kow  [Ber.  27,  Ref.  309,  941  (1894)]  was  able  to  bring  about 
the  addition  of  these  substances  to  olefins  in  the  presence 
of  zinc  chloride,  etc.  The  external  conditions  must,  how- 
ever, be  regulated  carefully  in  order  to  obtain  the  desired 
products;  that  is  to  say,  to  have  the  intermediate  addition 
compound  dissociate  along  the  lines  of  the  necessary 
equilibrium. 

Since  some  of  the  oxides  of  nitrogen  may  be  looked  upon 
as  similar  in  constitution  to  anhydrides  of  oxygen  acids,  it  is 
readily  understood  why  addition  products  can  be  obtained 
from  these  oxides  and  the  olefins.  When  nitrogen  trioxide 


OLEFINS  AND  THEIR  REACTION  PRODUCTS.      147 

is  passed  into  a  cooled  ethereal  solution  of  trimethylethylene, 

amylene  nitrosonitrite,  (CH3)2  C  —  CHCH3,  is  formed. 

I         I 
ON  -  O      NO 

A  compound  such  as  this  is  subject  to  tautomeric  change 
and  polymerization.  For  further  details  concerning  these 
reactions,  the  reader  is  referred  to  books  on  the  chemistry 
of  the  ter penes. 

When  acids  add  to  olefins,  the  olefinates  formed  may  be 
termed  salts  or  esters.  The  formation  of  olefinates  is 
therefore  one  form  of  esterification  similar  in  principle  to 
the  formation  of  ammonium  salts  and  of  hydrates  of  acids 
or  oxonium  salts.  Similarly,  the  hydration  of  olefins  to 
form  alcohols  and  ethers  really  belongs  to  the  same  class 
of  reactions,  alcohols  and  ethers  from  this  point  of  view 
being  esters  of  the  acid  water.  So  far  the  olefinates,  the 
alkyl  halides,  have  been  considered  in  some  detail.  Accord- 
ing to  the  terminology  in  general  use,  these  are  esters  formed 
from  organic  alcohols  and  inorganic  acids,  the  hydrogen 
halides.  The  esters  formed  with  organic  acids  will  now  be 
taken  up  in  the  same  way  first,  and  then  the  general 
question  of  esterification  will  be  considered. 

The  formation  of  esters  with  organic  acids  has  been 
studied  in  detail  with  the  olefin,  amylene.  This  is  doubtless 
due  to  ease  of  manipulation  and  experimental  technic  in 
general.  The  results  with  this  olefin  may  be  carried  over 
to  other  olefins,  and  the  general  principles  will  hold  for  all. 

D.  Konowalow  [Ber.  18,  2808  (1885)]  showed  that  gaseous 
amyl  acetate  dissociated  at  180°  with  appreciable  velocity 
when  substances  like  asbestos,  barium  sulfate,  glass  wool, 
etc.,  were  present.  N.  Menschutkin  [Ber.  15,  2512  (1882)] 
had  observed  that  this  ester  dissociated  into  amylene  and 
acetic  acid,  even  in  the  liquid  state  at  a  comparatively  low 
temperature,  and  that  the  velocity  of  this  dissociation 
increased  as  the  reaction  proceeded.  D.  Konowalow  [Z. 


148  CHEMICAL  REACTIONS. 

physik.  Chem.  1,  63  (1887)]  showed  this  auto-catalytic 
action  to  be  due  to  the  increasing  concentration  of  acid 
which  was  formed  in  the  reaction,  and  that  the  stronger  the 
acid  (the  more  highly  ionized  in  aqueous  solution)  so  formed, 
the  greater  its  action  [Z.  physik.  Chem.  8,  6  (1888)].  Thus, 
the  amyl  ester  of  trichloracetic  acid  dissociated  more 
rapidly  than  the  amyl  ester  of  acetic  acid.  The  addition  of 
hydrogen  halide  also  caused  the  dissociation  of  amyl 
acetate,  with  the  subsequent  formation  of  amyl  halide. 
The  equations  showing  these  changes  are  as  follows: 

[Am   ~j 
HAcJ 
iHAcI        rAm"| 


=  Am+HAc+HX 

W.  Nernst  and  C.  Hohmann  [(Z.  physik.  Chem.  11,  352 
(1893)]  showed  that  in  the  reaction  between  olefin  and  acid 
to  form  ester,  the  stability  of  the  ester,  as  measured  by  the 
equilibrium  constant 

r      r 

=  K 


tester 

increased,  and  the  value  of  the  constant  K  decreased,  with 
the  strength  of  the  acid.  Similar  conclusions  were  reached 
by  J.  Kendall  [J.  Am.  Chem.  Soc.  36,  1722  (1914)]  and 
others.  Nernst  and  Hohmann  also  showed  that  the  velocity 
of  formation  of  amyl  trichloracetate  from  amylene  and  the 
acid  was  proportional  to  the  square  of  the  concentration  of 
the  acid.  In  benzene  as  solvent,  the  velocity  was  greatly 
increased,  because  of  the  association  of  the  acid;  in  ether, 
on  the  other  hand,  the  velocity  was  less,  the  acid  not  being 
associated  in  it.  At  the  same  time  it  is  probable  that  the 
ether  and  the  trichloracetic  acid  form  a  complex,  indicated 
perhaps  by  the  following  equilibria: 


OLEPINS  AND  THEIR  REACTION  PRODUCTS.      149 


t  AcOHl      TAcOH 

+nEt2°= 


The  influence  of  benzene  and  ether  as  solvents  on  the 
velocity  of  the  ester  formation  is  similar  to  their  influence 
on  the  reaction  between  triethylamine  and  ethyl  iodide 
described  in  Chapter  V. 

Just  as  zinc  chloride  accelerates  the  reaction  between  an 
olefin  and  water  to  form  the  alcohol  and  the  reverse  re- 
action, so  also  does  it  accelerate  similar  reactions  in  which 
an  acid  or  an  alkyl  halide  takes  the  place  of  the  water. 
J.  Kondakow  [J.  pr.  Chem.  48,  479  (1893)]  found  that  when 
zinc  chloride  was  added  to  a  solution  of  trimethylethylene 
and  acetic  acid,  an  addition  compound,  C5Hi0.ZnCl2.- 
(HOAc)s  crystallized  out.  Treated  with  water,  this  addi- 
tion compound  yielded  amyl  acetate.  By  altering  the  con- 
ditions so  as  to  obtain  the  maximum  yield,  that  is,  by 
isolating  this  intermediate  addition  compound,  and  treating 
it  with  water,  Kondakow  was  able  to  obtain  a  20  per  cent. 
yield  of  ester,  although,  ordinarily,  in  the  equilibrium  mix- 
ture containing  amylene,  acetic  acid,  and  amyl  acetate, 
only  2  per  cent,  of  ester  was  present  (Nernst  and  Hohmann)  . 
If  the  reaction  mixture  was  allowed  to  stand  for  some  time 
before  water  was  added,  a  considerable  amount  of  diamylene 
was  formed.  The  reaction  may  be  formulated  as  follows: 
xC5Hio  +  yHOAc  +  zZnC!2 


r(C5H10),  ]  =  a  +  zZnC!2 

=    (HOAc)J         LHUACJ 

|_(ZnCl2)2  J  =  b  [™  J  +  yHOAc  +  zZnC!2 


(HOAc)     +  nH20  = 

n^r\  i 
L(ZnCl2)2 


c6H1 


150  CHEMICAL  REACTIONS. 

The  other  equilibria  which  are  possible  with  these  substances 
are  not  given.  They  would  be  similar  to  the  equilibria  in 
which  sulf  uric  acid  is  present  in  place  of  zinc  chloride,  which 
were  given  on  a  preceding  page.  In  this  reaction,  the  zinc 
chloride  plays  the  same  part  as  the  extra  molecule  of  acetic 
acid  in  the  associated  acetic  acid  in  the  formation  of  amyl 
acetate,  the  only  difference  being  that  the  zinc  chloride 
addition  compound  under  the  conditions  of  its  formation, 
does  not  form  appreciable  amounts  of  ester,  but  only  when 
treated  with  water.  A.  Behal  and  A.  Desgrez  [C.  r.  114, 
676  (1892)]  have  used  this  method  for  the  formation  of 
esters  of  higher  olefins. 

Since  the  esters  of  organic  acids  are  olefinates,  it  is  clear 
why,  in  the  distillation  of  esters  like  the  waxes,  etc.,  where 
a  high  temperature  is  necessary,  olefins  are  often  formed : 

CisHaiCC^CisHsT  =  CisHsiCC^H  +  CigHse. 

So  far  esters  have  been  considered  only  in  relation  to  their 
formation  from  olefins  and  acids.  The  usual  method  for 
preparing  esters  consists  in  the  action  of  an  alcohol  on  an 
acid  in  the  presence  of  a  catalyst.  The  mechanism  of  this 
reaction  has  been  studied  extensively  in  recent  years,  and 
all  the  evidence  indicates  the  formation  of  intermediate 
addition  compounds  in  the  reaction.  The  most  direct 
evidence  of  the  existence  of  such  intermediate  compounds 
composed  of  alcohol,  acid,  and  catalyzing  inorganic  acid 
was  given  by  G.  Baume  and  G.  P.  Pamfil  [J.  Chim.  Phys. 
12,  260  (1914)]  and  by  J.  Kendall  and  J.  E.  Booge  [J.  Am. 
Chem.  Soc.  88, 1712  (1916)].  Kinetic  studies  by  J.  Stieglitz 
and  by  H.  Goldschmidt  showed  that  addition  products 
must  be  assumed  to  be  present  in  the  reaction  mixtures, 
but  the  exact  nature  of  these  products  could  not  be  deter- 
mined. 

From  what  has  been  said  of  the  mechanism  of  reactions 
so  far,  it  may  be  stated  that  esterification  from  the  point 


OLEFINS  AND  THEIR  REACTION  PRODUCTS.      151 

of  view  of  the  addition  theory  may  be  placed  in  parallel 
with  the  neutralization  of  an  acid  by  a  base.  Both  reactions 
belong  to  the  general  type  of  reaction  given  earlier: 

AnMX  +  H2O  =  AnMH2OX  =  AWMOH  +  HX 


>  II 

>  III 

< IV 

< V 

I.  Neutralization;   II.  Hydration;   III.  Hydrolysis  or  dis- 
sociation;   IV.  Dehydration  or  dissociation;   V.  Addition. 
In  the  formation  of  a  salt  from  an  acid  and  a  base  accord- 
ing to  I,  the  reaction  would  be: 


HA  +  MOH  =  1  =  MA  +  H2O;  (a) 

and  in  the  formation  of  an  ester  from  an  acid  and  an 
alcohol,  the  reaction  would  be: 


HA  +  ROH  =         :        =  RA  +  H20.  (6) 

J 


The  presence  of  a  third  substance  which  is  capable  of 
forming  addition  compounds  with  the  reacting  components 
may  accelerate  greatly  both  sets  of  reactions.  In  -(a), 
water  serves  the  purpose,  and  acts  therefore  as  the  catalyst 
for  this  reaction;  in  (6)  some  other  substance  such  as 
sulfuric  acid  or  hydrogen  chloride  may  produce  a  similar 
effect.  The  formulations,  including  the  catalysts  may  be 
given  as  follows: 


fHOH-| 
+  [cat.  J  \ 


RA+Cat.  H20+Cat. 
11 


152  CHEMICAL  REACTIONS. 

For  the  particular  reactions  in  question,  these  would  be- 
come: For  (a) 


HA+H20=  IHOH 


rHA  i+r 

LHOH] 


MORI     HA 


rMoin 


MOH   HMA]+2H2° 
2HOH        LMAJ  =  MA+H20 


HOH  J 

(dehydration,  if  MA  is  insoluble,  etc.). 


For  (6) 

HA+  HC1  =  ,        ROH  +  HC1  =  ]  > 


HA  I         ROH1 


RA  1        HOHl 


Since  the  neutralization  of  an  acid  by  a  base  takes  place 
practically  instantaneously,  and  since  this  reaction  has 
been  explained  in  past  years  as  due  to  ions,  rapid  reaction 
has  been  taken  to  be  a  characteristic  property  of  ionic 
reactions.  Other  reactions  in  aqueous  solution  have  also 
been  taken  to  bear  out  this  view.  It  was  shown  previously 
how  the  addition  theory  explains  the  neutralization  reac- 
tion; the  same  explanation  applied  to  esterification  shows 
the  advantage  of  a  common  viewpoint  for  the  two  sets  of 
reactions.  The  differences  in  velocities  of  the  two  may  be 
explained  as  due  to  the  difference  in  efficiency  of  the  two 
catalysts,  water  and  acid,  which  is  in  turn  related  to  the 
formation  of  the  intermediate  addition  compounds  and 
their  properties. 

In  the  formation  of  esters  in  absolute  alcohol,  it  has  been 
found  that  salts  such  as  zinc  chloride  increase  the  formation 
of  esters  especially  when  hydrogen  chloride  is  also  present. 
This  is  one  of  the  common  methods  used  in  esterification. 
R.  Engel  (cf.  Werner,  p.  113)  pointed  out  that  the  addition 


OLEFINS  AND  THEIR  REACTION  PRODUCTS.      153 


of  one  molecule  of  hydrogen  chloride  to  a  molecule  of  zinc 
chloride  caused  at  the  same  time  the  addition  of  at  least 
two  molecules  of  water  to  form  the  compound  ZnCfeHCL- 
2H2O.  Just  as  with  the  platinic  chloride  compounds  with 
hydrogen  chloride  or  water  or  both,  hydrogen  is  found  in  the 
outer  zone.  Since  water  and  alcohol  are  very  much  alike 
in  many  respects,  it  is  possible  that  where  absolute  alcohol 
serves  as  the  solvent,  the  salt  effect  of  the  zinc  chloride  is 
similar  to  the  salt  effect  in  aqueous  solutions. 

For  the  further  discussion  of  similar  reactions,  the  reader 
is  referred  to  Chapter  VI.  In  general,  the  term  hydrolysis 
is  taken  to  mean  the  decomposition  of  a  substance  by 
water.  Since  water  is  one  of  the  products  in  the  formation 
of  esters  from  alcohols  and  acids,  hydrolysis  becomes  the 
reverse  reaction  of  esterification  in  this  case.  Therefore 
what  has  already  been  stated  concerning  esterification 
applies  also  to  hydrolysis. 

Since  water  is  closely  related  to  the  alcohols,  it  is  not 
surprising  that  in  certain  reactions  alcohols  play  a  part 
similar  to  that  of  water  in  hydrolysis.  Thus,  instead  of: 


HOH  +  En.HA  = 


the  following  may  be  written : 

TEn 
En 
HA 
HOH 


EnHOH  +  EnHA  = 


[HOH 
[En 

HOH 


HA] 


and,  as  examples  of  such  reactions  may  be  cited : 

EtOH  +  EtI  =  EtOEt  +  HI, 
CH3.COOC5Hn  +  CH3OH  =  CH3COOCH3  +  C5HnOH. 

Among  other  methods  used  in  the  formation  of  esters  may 
be  mentioned  the  acylation  of  alcohols  by  means  of  acid 


154  CHEMICAL  REACTIONS. 

chlorides  and  acid  anhydrides.  These  reactions  really  be- 
long to  the  same  type  as  the  others,  as  can  be  seen  from  the 
following  equations:  (Cf.  D.  Konowalow,  Z.  physik.  Chem. 
jf,  67  (1887)) 

AC1    1  =  AOH.En+HCl 
AC1  +  EnHOH  =     En 

=  EnHCl  + AOH 


It  is  evident  that  this  is  only  an  alcoholysis  of  the  acid 
chloride,  and  corresponds  to  reaction  III  above.  In  a 
great  many  cases  alkali  aids  in  the  formation  of  esters  by 
this  method.  This  corresponds  to  the  addition  of  alkali 
to  an  aqueous  solution  of  a  salt  to  aid  its  hydrolysis.  The 
latter  is  generally  explained  on  the  ionic  basis  as  due  to 
increasing  the  concentration  of  OH~~.  It  might,  however, 
be  explained  equally  well  by  the  formation  of  the  inter- 
mediate addition  compound,  which  then  dissociates  into 
water,  and  the  salt  of  the  acid  and  alkali  used.  In  other 
words,  it  favors  the  equilibrium  for  hydrolysis,  by  removing 
the  acid  as  fast  as  it  is  liberated. 

When  acid  anhydrides  are  used  instead  of  acid  chlorides, 
the  acid  group,  OOCR,  plays  the  same  part  as  the  halide  in 
the  acid  halide.  What  has  been  said  with  regard  to  acid 
halides  and  their  alcoholysis,  applies  also  to  the  anhydrides 
and  their  alcoholysis. 

Instead  of  alkali,  other  substances  such  as  pyridine, 
quinoline,  aniline,  etc.,  may  be  used.  In  the  case  of  these 
substances,  experimental  evidence  shows  that  the  pyridine, 
for  example,  combines  with  the  acid  halide.  The  simplest 
way  of  writing  the  reaction  taking  place  would  be : 

"En      " 
HOH         [En     "I       [Py    ~] 

ACI      =  LHOAJ+  |_HCi_r 

Acid  chlorides,  etc.,  of  inorganic  acids  also  react  with 


OLEFINS  AND  THEIR  REACTION  PRODUCTS.      155 

alcohols  to  form  esters  of  the  acid  or  of  the  hydrogen  halide. 
The  reaction  between  alcohols  and  phosphorus  halides  are 
examples  of  this  kind. 


HOH1 

ci3  J 


=  HOPC12  +  HC1, 


En 

HOH 

PC13 


_[-HOPCl2-| 
|_En 


HOPC12  + 


l-En-l' 
LHClJ 


PC15  +  PhOH  =  Cl2P(OPh)3 

(W.  Autenrieth  and  A.  Geyer,  Ber.  41,  146  (1908)), 

ROH  +  PC15  ->  ROPCU  +  HC1  1 
ROPCU  ->  RC1  +  POC13  J 

(W.  Anschiitz  and  W.  O.  Emory,  Lieb.  Ann.  253,  120). 
The  reaction  between  aluminium  chloride  and  alcohols  is 
similar  in  character,  as  follows: 

Aids 

A1CU  +  SEn.HOH  =     3En         =  +  3HC1; 

LEn3 


etc. 

The  formation  of  ethers  may  be  considered  from  the 
same  point  of  view  as  the  formation  of  esters.  This  was 
indicated  in  connection  with  the  reaction  between  ethylene 
and  water,  with  sulfuric  acid  as  catalyst,  where  the  produc- 
tion of  ether  was  shown  in  one  of  the  equilibria.  The 
reaction  between  alcohol  and  sulfuric  acid  to  form  ethyl 
sulfuric  acid,  and  then,  with  more  alcohol,  ether,  is  also  of 
historical  interest. 

The  reactions  between  ethylene,  water,  and  sulfuric  acid, 
in  which  it  was  shown  the  products  which  may  be  formed, 
were  given  on  a  previous  page  and  need  not  be  repeated 
here.  Ether  is  formed  according  to  equilibrium  (5),  if 
the  external  conditions  are  suitable,  and  the  substances 
present  in  suitable  concentrations. 

The  graphic  formula  for  ether  is  based  mainly  upon  the 


156  CHEMICAL   REACTIONS. 

proof  of  the  structure  for  alcohol  as  ROH.  The  latter 
rests  upon  the  proof  that  one  atom  of  hydrogen  acts 
differently  from  the  rest  when  treated  with  a  metal  like 
sodium,  and  that  a  hydroxyl  is  present,  as  shown  by  treat- 
ment with  phosphorus  halide.  As  shown  in  a  former  chap- 
ter with  acids,  tautomerism  is  possible  and  the  alcohol 

may   react   in   the   form        -,C==tO    just   as   acids   do. 

H  H 

lonization  is  not  probable  for  this  compound,  since  posi- 
tive hydrogen  is  combined  with  carbon  predominatingly 
negative. 

This  brings  up  the  question  of  the  structures  of  organic 
acids,  which,  while  not  pertinent  to  the  subject  under  dis- 
cussion, still  may  be  interpolated  in  this  place.  Up  to  this 
point,  the  acyl  group  in  organic  acids  has  been  treated  as 
a  unit  and  generally  indicated  by  the  letter  A.  The  re- 
semblance of  acyl  halides  to  alkyl  halides  in  their  reactions 
with  amines  and  alcohols,  etc.,  the  similarity  between 
ethers  and  esters,  and  between  amines  and  amides,  points 
strongly  to  a  similarity  in  chemical  makeup  or  constitution. 
This  relationship  can  be  most  simply  expressed  or  accounted 
for  by  considering  the  organic  acids  as  water  which  is  not 
only  olefinated,  as  in  the  case  of  alcohols,  but  as  also  having 
carbon  monoxide  combined  with  it,  and  thus  giving  them 

rco   I 

the  structure     HOH    ,  the  carbon  monoxide  being  an  un- 

[En     J 

saturated  compound  like  water,  olefin,  ammonia,  etc.  Be- 
cause of  tautomeric  changes  within  these  addition  com- 
pounds, just  as  in  the  hydrates  and  ammoniates  of  platinic 
chloride  and  the  oxygen  acids,  sulfuric  and  nitric  acids,  the 
atoms  may  occupy  different  positions  in  the  molecule. 

Ico  "I          o  o 

HOH          =    ||    xEn— H       =  lxH** 

[En  J  C^-*OH  O=  C-« — H      En 

(1)"  (2)  .      (3) 


OLEFINS  AND  THEIR  REACTION  PRODUCTS.      157 


Formula  (2)  corresponds  to  the  structure  which  is  used  in 
organic  chemistry  at  present,  the  proof  for  which  is  out- 
lined in  Meyer  and  Jacobson's  Lehrbuch  der  organischen 
Chemie  ((1907)  Vol.  1,  p.  76)  and  other  textbooks.  The 
reactions  cited  in  this  proof  of  structure  may  in  general 
be  applied  equally  well  to  all  three  structures.  The  con- 
sideration of  the  three  structures  shows  a  closer  relationship 
between  organic  acids  and  inorganic  acids  than  does  struc- 
ture (2)  alone. 

Carbon  monoxide  bears  the  same  relation  to  formic  acid 
that  sulfur  trioxide  bears  to  sulfuric  acid,  or  that  platinic 
chloride  bears  to  chlorplatinic  acid,  etc.  Carbon  monoxide 
also  bears  the  same  relation  to  the  higher  organic  acids 
such  as  acetic,  propionic,  etc.,  acids  that  sulfur  dioxide 
bears  to  the  sulfonic  acids,  or  that  the  anhydride  of  nitrous 
acid  bears  to  the  nitro  compounds,  etc. 


H 

tl 
En 


9 
A 


OH 


OH 


X 


En 


\\ 

En 


Organic  acid 


Sulfonic  acid  Nitro  compound. 


Furthermore,  by  the  aid  of  these  structures,  it  is  possible 
to  recognize  the  relationship  between  acid  halides,  esters, 
amides,  and  the  acids  themselves,  more  readily: 


HOH] 

rncr 

"HOH  En] 

"NH3" 

CO 

CO 

CO 

CO 

En 

[En 

En 

En 

or 


CO 

CO 

CO 

CO 

EnH    OH 

/\ 

EnH    Cl 

/  V 
EnH    OR 

/\ 

EnH    NH2 

acid 

chloride 

ester 

amide 

Formic  acid  differs  from  the  other  acids  of  the  organic 
series  in  being  simply  hydrated  carbon  monoxide.     This 


158  CHEMICAL  REACTIONS. 

structure  for  formic  acid  agrees  with  all  the  properties  of 
the  acid.  It  is  not  at  all  surprising  that  its  dissociation  into 
carbon  monoxide  and  water  is  effected  by  catalysts  such  as 
hydrochloric  acid,  etc.  (G.  E.  Branch,  Jour.  Amer.  Chem. 
Soc.  37,  2316  (1915)),  since  it  is  an  addition  reaction,  similar 
to  the  formation  of  ammonium  chloride  from  ammonia  and 
hydrogen  chloride.  The  explanation  for  the  decomposition 
of  formic  acid  into  carbon  dioxide  and  hydrogen  is  evident 
from  formula  (3)  for  acids  given  above. 
H  O 

f         —  H2  +  C02 


This  reaction  involves  oxidation-reduction  and  will  there- 
fore be  discussed  more  fully  in  a  later  chapter.  The  other 
organic  acids,  such  as  acetic  acid,  etc.,  behave  in  the  same 
way  when  heated  with  concentrated  sulfuric  acid,  or  in 
some  cases  when  heated  alone  [W.  Oechsner  de  Coninck, 
C.  r.  136,  1069  (1903)]. 

CH3COOH  =  CH4  +  CO2 


EnH  O 

XC         =EnH2  +   CO3 


Aromatic  acids  can  also  be  included  under  the  structures 
given.  With  them,  the  phenylene  group  plays  the  same 
part  as  the  olefin  with  the  aliphatic  acids. 

Oxalic  acid  would  have  the  following  structure;   that  of 
a  mixed  acid  similar  to  dithionic  acid. 

CO    ]  FSOs    ] 

HOH    oxalic  acid,    HOH    dithionic  acid. 

CO,    \  LS03    J 

This  indicates  the  dissociation  of  oxalic  acid  into  carbon 
monoxide  and  carbon  dioxide,  and  of  dithionic  acid  into 
sulfur  dioxide  and  sulfuric  acid. 


OLEFINS  AND  THEIR  REACTION  PRODUCTS.      159 

If  the  explanation  of  the  relation  between  alcohols  and 
ethers  is  accepted,  it  becomes  easier  to  understand  alkyl 
compounds  and  their  reactions  in  general.  They  fall  into 
the  same  class  as  the  ammoniates  and  the  hydrates,  and 
may  be  called  olefinates.  Alcohol  and  ether  are  water 
olefinated  to  different  degrees.  Their  constitutions  may 
be  expressed  as  follows  (01  :  olefin)  :  Alcohol,  Ol.HOH; 
ether,  O^.HOH;  alkyl  iodide,  Ol.HI;  ethyl  sulfuric  acid, 
En.H2S04;  etc.  The  reaction  for  the  formation  of  ethyl 
ether  may  be  expressed  as  follows: 


En.HOH  +  Na  = 


En.HONa  +  En.HI  = 


]  +  H, 


En      ]       rr, 
HOH     =  [?*.. 
Na     J       LHONa 
En2      "1      r  -. 

2?Na  =[Son]+NaI- 


HI 


This  explanation  indicates  that  the  action  of  sodium 
upon  alcohol  is  really  the  action  of  sodium  upon  water, 
partially  olefinated.  The  action  of  ethyl  iodide  upon 
sodium  ethoxide  is  not  the  replacement  of  the  sodium  by 
ethyl  so  much  as  the  action  of  olefinated  hydrogen  iodide 
upon  olefinated  sodium  hydroxide.  It  is  the  same  type  of 
reaction  as  the  neutralization  of  sodium  hydroxide  by 
hydriodic  acid  in  aqueous  solution.  The  hydrated  hydro- 
gen iodide  reacts  with  hydrated  sodium  hydroxide.  The 
water  bears  the  same  relation  to  the  latter  reaction  that 
the  olefin  does  to  the  former. 

The  difference  in  properties  of  the  various  compoundated 
hydrogens  can  be  shown  by  a  comparison  of  the  following 
compounds:  ethyl  iodide,  ammonium  iodide,  and  oxonium 
iodide.  Ethyl  iodide  requires  the  highest  temperature  for 
its  dissociation  and  the  hydrate  of  hydrogen  iodide  the 
lowest.  This  shows  why  hydrogen  is  evolved  if  a  metal  is 
dissolved  in  an  aqueous  solution  of  an  acid,  or  if  a  metal  such 


160  CHEMICAL  REACTIONS. 

as  magnesium  is  dissolved  in  a  solution  of  an  acid  such  as 
hydrogen  chloride  in  liquid  ammonia,  while,  if  a  metal 
like  sodium  or  magnesium  is  dissolved  in  an  ethereal  solu- 
tion of  an  alkyl  halide,  the  olefinated  hydrogen  is  evolved. 
(The  ether  in  the  Grignard  reaction  plays  the  same  part  as 
the  water  in  an  aqueous  solution  of  the  hydrated  hydrogen 
iodide,  the  excess  of  liquid  ammonia  in  the  ammoniacal 
solution  of  the  ammoniated  hydrogen  iodide,  and  if  it  were 
possible  to  have  a  solution  of  hydrogen  iodide  in  liquid 
ethylene,  containing  an  excess  of  ethylene,  this  ethylene 
would  very  likely  act  just  as  the  solvent  ether  does.) 

Ethers  are  generally  spoken  of  as  inert  compounds. 
What  is  really  meant  is  that  they  do  not  react  with  metals, 
alkalies,  and  most  acids  at  ordinary  temperatures  with 
appreciable  velocity.  As  pointed  out,  the  properties  of 
the  olefinated  hydrogen  afford  an  explanation.  The  same 
holds  true  for  tertiary  amines.  It  has  already  been  pointed 
out  that  a  difference  is  shown  in  the  stability,  or  better, 
the  reactions  of  the  olefinated  hydrogen  depending  upon 
the  other  substances  present.  Thus,  in  the  presence  of 
chlorides,  such  as  zinc  chloride,  etc.,  ethyl  iodide  reacts 
less  rapidly  than  the  chloride.  The  same  relative  order  was 
observed  with  ammonium  chloride,  bromide,  iodide,  and 
hydroxide.  The  decomposition  of  ethers  by  heating  with 
hydrogen  iodide,  a  method  used  for  the  determination  of 
the  amount  of  ether  groups  present  in  compounds,  may  be 
explained  on  the  same  basis.  They  are  simple  displacement 
reactions.  The  existence  of  the  intermediate  addition  com- 
pounds (oxonium  salts)  has  been  proven: 


1+lffll 

En2.HOH  +  HI  -  '  ™™  '         L — "J 


En 
HOH 


Other  acids  are  capable  of  decomposing  ethers.     Concen- 


OLEFINS  AND  THEIR  REACTION  PRODUCTS.      161 

trated  sulfuric  acid  dissolves  ether  with  the  evolution  of 
considerable  heat,  and  if  the  mixture  is  heated  for  some 
time  at  100  degrees,  ethyl  sulfuric  acid  and  ethyl  sul- 
fate  are  formed.  Also  acid  chlorides  react  similarly  with 
ethers. 


The  reaction 

/CH3C1  +  CH3COOC5Hn 
2CH3OC5Hn  +  2CH3COCl( 

VyEtnCl  +  CH3COOCH3 

may  be  quoted  as  example  (F.  Wedekind  and  J.  Hausser- 
mann,  Ber.  34,  2081  (1901)). 

The  amines  differ  from  the  ethers  and  alcohols  in  that 
they  are  olefinated  ammonia  or  ammoniated  olefins.  What 
has  been  said  with  regard  to  ethers  and  alcohols  applies 
also  in  a  general  way  to  the  amines.  Primary  and  secondary 
amines  correspond  to  the  alcohols  while  the  tertiary  amines 
correspond  to  the  ethers.  Because  of  properties  of  the 
aminated  compounds  or  ammonium  salts  as  compared  with 
the  oxonium  salts  or  etherates  these  two  series  of  com- 
pounds as  a  rule  are  looked  upon  from  entirely  different 
standpoints.  With  the  nitrogen  series,  the  properties  of 
the  central  nitrogen  atom  of  the  aminates  and  ammoniates 
predominate,  while  in  the  oxygen  series  the  properties  of 
the  olefinated  hydrogen  and  also  of  the  hydrogen  with  the 
alcohols  are  more  prominent  than  those  of  the  central  oxygen 
atom.  It  is  only  in  recent  years  that  much  attention  has 
been  paid  to  the  etherates  and  in  general  to  the  oxonium 
salts. 

Because  of  the  properties  of  the  ammonium  salts  and 
aminates  which  permit  of  their  existence  under  ordinary 
conditions,  it  is  much  easier  to  show  the  mechanism  involved 
in  the  formation  of  amines,  than  in  the  corresponding 


162 


CHEMICAL  REACTIONS. 


cases  of  the  alcohols  and  the  ethers.  It  has  been  possible 
to  show  the  occurrence  of  the  intermediate  addition  com- 
pound at  ordinary  temperatures  with  the  nitrogen  com- 
pounds, while  with  the  oxygen  compounds  lower  tempera- 
tures, and  the  application  of  the  principles  of  the  Phase 
Rule  were  necessary  to  prove  the  existence  of  such  com- 
pounds. The  formation  of  amines  from  ammonia  and 
alkyl  halides  may  be  represented  by  the  following  equations, 
which  differ  only  slightly  from  the  way  A.  W.  Hofmann 
originally  expressed  the  reactions: 

En    1       rp      -i 

=  |_NH3J  +  HX    10amine> 


En.HX  +  NH3 


En.HX  +  En.NH3 


En.HX  +  En2NH3 


NH3 
HX 


NH3 

HX 

En3 

NH3 

HX 


2°  amine, 
3°  amine. 


The  acid  of  the  alkyl  halide  plays  the  same  part  in  the 
formation  of  amines  as  it  does  in  the  formation  of  ethers. 
This  is  emphasized  in  the  formation  of  diphenylamine  from 
aniline  hydrochloride  and  aniline 

Ph2NH 
PhNH,HCl  +  NH2Ph  = 


NH3       (Pen  =  Phenylene) 

The  reason  for  not  considering  the  acid  of  the  alkyl  halide 
to  play  this  part  in  the  formation  of  ethers,  is  to  be  found 
in  the  intermediate  addition  compound,  the  alkyl  am- 
monium salt,  which  combines  with  the  acid  so  that  under 
ordinary  conditions  the  latter  is  not  liberated  and  allowed 
to  go  through  the  cycle  again.  Even  in  the  formation  of 
the  diphenyl  amine  where  the  intermediate  compound  dis- 


OLEFINS  AND  THEIR  REACTION  PRODUCTS.      163 

sociates,  the  acid  is  taken  up  by  the  ammonia,  and  thus 
prevented  from  acting  as  the  catalyst.  It  will  be  recalled 
that  in  the  chapter  on  catalysis  it  was  pointed  out  that 
platinic  chloride  might  act  as  the  catalyst  in  the  formation 
of  ammonium  chloride  from  ammonia  and  hydrogen  chlor- 
ide, if  the  conditions  were  such  that  the  intermediate  com- 
pound dissociated  and  liberated  the  platinic  chloride. 

Since  ethers  may  be  formed  from  two  molecules  of  alcohol, 
and  secondary  and  tertiary  amines  from  two  molecules  of 
amines  of  lower  order  it  should  be  possible  to  combine 
alcohols  and  amines.  Such  compounds  have  been  formed 
by  treating  alcohols  with  ammoniated  zinc  chloride  (V. 
Merz  and  K.  Gasiorowski,  Ber.  11,  623  (1884)). 

ROH  RNH2 

or  NH3   1  or  H2O 


or  fNH3   '  or 

[En     1+LznClJ  =  TEn   1  + 

LHOHJ  LNHsJ 


H.  Goldschmidt  and  C.  Wachs  (Z.  physik.  Chem.  24, 
353  (1897))  showed  that  the  formation  of  amides  (anilides) 
followed  the  same  laws  as  the  formation  of  esters.  With 
both,  the  reaction  is  bimolecular  in  the  absence  of  a  strong 
acid,  being  autocatalyzed  by  the  organic  acid  itself.  The 
amine  plays  the  same  part  in  the  formation  of  an  amide 
as  the  alcohol  in  the  formation  of  an  ester.  Instead  of  an 
oxygen  ester,  a  nitrogen  ester  is  formed.  The  same  relations 
apply  to  both,  and  they  may  be  formulated  similarly. 


FEn      -I 

LHOHJ 

FEn  1 
LNHSJ 


HOA  = 


HOA  = 


H20. 


If  the  catalyst  is  taken  into  account,  the  following  equations 
may  be  given:  If  no  strong  acid  is  present: 


164 


CHEMICAL  REACTIONS. 


LHOHJ 


"En 

(HOA)n=    HOH 
.(HOA)n 

[En 

=    NH3 
L(HOA)n 

With  an  acid  HX  present: 


=  [-En     I 
l_H2NAj 


rHOH 
L(HOA)n_J 


[ 


En 
HOH 


"En 

f"HOH"l 

"Fn 



JBuI 

HOH 

_HOA_ 

LHX  J 

HOA 
HX 

= 

"En 
HOA 
HX 

raoHi 
LHOAJ 

1! 

HOA, 


l-En      1+fHOAl 

LHNH2J    LHX  . 


'En 

HNH2 
HOA 

-Pn  1+ 

|_H2NA_r 

HX 

Amides  may  also  be  formed  by  other  methods  similar  to 
the  methods  used  for  the  acylation  of  alcohols,  that  is,  with 
acyl  halides  and  acid  anhydrides: 

'En 


LNH3J 


A(OA)  = 


The  formation  of  amides  from  ammonium  salts  of  oxygen 
acids  is  in  fact  only  a  part  of  the  dissociation  of  the  inter- 
mediate addition  compound  in  amide  formation  from  an 
amine  and  an  acid.  The  formation  of  amide  from  ester 
and  ammonia  is  similar  to  the  formation  of  amide  from 


OLEFINS  AND  THEIR  REACTION  PRODUCTS.       165 
a  mine  and  acid  except  for  the  olefinated  acid  in  place 


of  the  acid: 


En 

AOH 

HNH 


AOH 


Amides  may  be  hydrolyzed  and  saponified  just  as  esters. 
This  is  only  the  reverse  reaction  to  their  formation.  Just 
as  with  the  esters,  amides  may  also  undergo  alcoholysis. 
The  reactions  are  as  follows: 


ANH 


[En     1 

LHOH| = 


En 
ANH2 

HOH 


=  AOH+[NH3] 
=  [AOH]  +  NH3 

(Meyer  and  Jacobson,  p.  609), 


"En 

[Sojn 

HP"'        1   = 

h  LHOHJ 

En' 
HO  A 

HOH 

TEn'  1 

LHOAJ 


En 


etc. 


CHAPTER  IX. 
OXIDATION-REDUCTION. 

IN  the  last  four  chapters  a  number  of  chemical  reactions 
were  taken  up  and  classified  according  to  certain  principles 
laid  down  in  the  earlier  chapters.  In  Chapter  V,  the 
general  consideration  of  reactions  was  outlined  and  some 
of  the  principles  elaborated.  Chapters  VI  and  VII  con- 
tained a  classification  of  reactions  based  upon  certain 
general  types  of  chemical  change,  the  actual  substances 
taking  part  being  subordinated  to  the  general  scheme.  In 
Chapter  VIII  the  point  of  view  was  shifted  in  that  the 
change  in  composition  of  the  substances  reacting  was 
emphasized.  The  various  reactions,  considered  before  from 
the  standpoint  of  type  of  reaction  were  here  developed  from 
the  position  of  the  reacting  substances,  and  as  the  special 
group  of  substances  chosen,  the  chemical  changes  undergone 
by  the  olefins  were  outlined.  In  these  four  chapters,  how- 
ever, one  important  limitation  was  introduced.  In  the 
reactions  and  compounds  which  were  taken  up,  none  of  the 
atoms  in  any  of  the  molecules  changed  its  state  of  oxidation. 
This  limitation  excluded  all  oxidation-reduction  reactions 
which  will  be  taken  up  in  this  and  the  following  chapters. 

It  seems  advisable  first  to  define  and  describe  the  phe- 
nomena of  oxidation  and  reduction  from  the  newer  chemical 
viewpoints,  and  then  to  apply  these  definitions  and  descrip- 
tions to  a  number  of  reactions. 

The  valence  of  an  element  is  defined  as  the  number  of 
negative  electrons  an  atom  of  that  element  loses  or  gains 
to  form  chemical  linkings.  Stated  in  somewhat  different 
terms,  the  valence  of  an  element  may  also  be  defined  as  the 
number  of  equivalents  of  the  acidic  or  of  the  basic  con- 
stituents combined  with,  or  associated  with,  one  formula 

166 


OXIDATION-REDUCTION.  167 

weight  of  that  element.  The  symbolism  used  heretofore 
in  this  book  and  which  applies  with  the  first  definition  will 
be  used  here  as  well.  The  production  of  every  chemical 
linking  involves  the  loss  of  (at  least)  one  electron  by  one 
atom  and  the  gain  of  (at  least)  one  electron  by  another 
atom.  The  formation  of  this  linking  will  therefore  involve 
a  simultaneous  oxidation  of  one  atom  and  reduction  of  the 
other.  Thus,  starting  with  a  neutral  hydrogen  atom  and  a 
neutral  chlorine  atom,  in  order  to  form  a  molecule  of 
hydrogen  chloride,  the  hydrogen  atom  loses  a  negative 
electron  and  acquires  a  positive  charge,  and  the  chlorine 
atom  gains  a  negative  electron  and  acquires  a  negative 
charge. 

Some  of  the  arguments  in  favor  of  such  a  polar  view  of 
valence  have  been  given  in  the  first  chapter.  The  conclu- 
sions with  regard  to  such  charged  atoms  were  not  specially 
emphasized  in  the  reactions  described  in  previous  chapters, 
but  it  is  evident  from  what  has  been  said  already,  that  the 
valence  of  an  atom  or  the  nature  of  its  electric  charge  is  of 
paramount  importance  and  significance  in  oxidation-reduc- 
tion reactions.  Change  of  valence  is  the  significant  feature 
of  oxidation  and  reduction;  the  participation  of  oxygen  or 
hydrogen  as  such  has  nothing  necessarily  to  do  with  the 
reaction. 

The  actual  charge  or  valence  of  an  atom  in  combination 
is  of  importance  in  the  reactions  to  be  considered,  and 
when,  under  certain  conditions  or  by  various  treatments, 
the  valence  is  changed,  the  mechanism  of  the  reaction 
involving  such  a  change  is  of  interest.  These  questions  are 
fundamental  and  will  be  considered  in  detail  as  occasion 
arises. 

The  experiments  described  in  Chapter  I  showed  that  in 

any    oxidation-reduction   reaction   involving   electrolytes, 

that  for  every  mol  of  an  element  undergoing  oxidation  or 

reduction,    96,500    coulombs   of    electricity   or    a    simple 

12 


168  CHEMICAL  REACTIONS. 

multiple  of  this  quantity  are  involved.  This  holds  true 
for  organic  substances  undergoing  oxidation  or  reduction 
as  well  as  for  inorganic  substances,  as  long  as  the  substance 
can  be  brought  into  solution  and  satisfactory  electrical 
measurements  made.  (A  practical  method  of  illustrating 
such  changes  is  by  means  of  the  "  Chemometer  "  described 
first  by  W.  Ostwald,  Z.  physik.  Chem.  15,  399  (1894).) 

In  the  equation  for  the  change  in  free  energy  or  the 
chemical  affinity  of  a  reaction  as  stated  in  Chapter  I, 

A  =  RT  log,  °yf,«'/'    -  RT  log,  K, 

l/l       02 

if  the  electromotive  force  of  a  galvanic  cell  in  which  the 
current  is  produced  by  the  chemical  reaction  is  denoted 
by  E,  and  one  gram  equivalent  of  the  substance  in  question 
is  transformed,  then 

E  =  A, 

under  similar  conditions  of  reversibility,  etc.,  under  which 
A  may  be  measured,  using  suitable  units.  W.  Nernst  de- 
veloped the  osmotic  theory  of  current  production,  showing 
the  mechanism  by  which  the  chemical  reactions  produced 
the  electric  current.  Thus,  the  difference  in  potential  of 
two  solutions  containing  univalent  ions  of  a  completely 
ionized  electrolyte  of  concentration  HI  and  r^  with  mobilities 
of  cation  and  anion  equal  to  u  and  v  (motion  under  a 
definite  potential  gradient)  is  given  by  the  equation 


In  an  analogous  manner,  for  the  solution  of  a  metal  in  a 
solution  of  its  salt,  E=RT\ogeP[p  when  one  gram 
equivalent  of  the  metal  acting  as  electrode  is  dissolved, 
in  which  P  represents  the  electrolytic  solution  tension  of 
the  metal,  and  p  the  osmotic  pressure  of  the  univalent  ion 


OXIDATION-REDUCTION.  169 

of  the  metal  in  the  solution.  In  place  of  the  pressures, 
P  and  p,  the  corresponding  concentrations,  C  and  c,  may 
be  used.  Similar  relations  may  be  developed  for  negative 
ions  and  elements.  A  comparison  of  the  electromotive 
forces  developed,  for  example,  with  metals  and  solutions  of 
their  ions  will  show  the  relative  oxidizing  or  reducing 
potentials  of  these  elements;  that  is,  the  chemical  affinities 
with  which  these  elements  enter  into  chemical  combination. 
As  pointed  out  before,  an  element  entering  into  chemical 
combination  forms  definite  chemical  linkings,  that  is  to  say, 
gains  or  loses  electrons.  These  electromotive  force  values 
are  fundamental  therefore  for  studying  the  chemical  affini- 
ties of  the  simplest  reactions.  The  theoretical  and  experi- 
mental developments  of  W.  Nernst  have  made  possible 
the  quantitative  study  of  the  phenomena  postulated  by  J. 
Berzelius  more  or  less  definitely  in  his  electrochemical 
theory.  N.  T.  M.  Wilsmore  (Z.  physik.  Chem.  S5,  291 
(1900))  calculated  from  the  best  data  available  the  relative 
electromotive  forces  shown  by  a  number  of  elements  as 
electrodes  against  solutions  containing  normal  concentra- 
tions of  their  ions.  These  are  known  as  the  decomposition 
potentials  and  are  based  upon  the  value  of  hydrogen  as 
zero.  These  values  can  be  used  to  determine  the  replace- 
ment of  metals,  etc.,  by  each  other,  the  electromotive  forces 
of  galvanic  combinations,  etc.  They  apply  directly  to  the 
concentrations  indicated.  For  other  concentrations  some- 
what different  values  must  be  used. 

The  quantitative  theory  of  electromotive  force  produc- 
tion and  its  relation  to  chemical  combination  outlined  very 
briefly  and  superficially  (for  more  exhaustive  treatments 
the  reader  is  referred  to  suitable  text  books  on  physical 
chemistry)  may  be  extended  to  chemical  phenomena  in 
general,  in  the  same  way  that  the  experimental  measure- 
ments of  valence  on  the  basis  of  the  ionic  theory  of  solutions 
were  extended  and  elaborated  in  the  electron  conception  of 


170  CHEMICAL  REACTIONS. 

valence  to  include  all  chemical  compounds.  Evidently 
this  comparison  is  deep-seated.  Since  all  chemical  com- 
pounds are  formed  by  the  transfer  of  electrons  producing 
the  linkings,  the  atoms  are  all  charged  electrically  in  these 
compounds.  The  chemical  affinity  may  then  be  con- 
sidered to  be  given  by  the  affinity  of  the  given  atom  for  an 
electron  under  the  conditions  pertaining  to  that  compound, 
or  in  other  words  by  a  value  which  might  be  said  to  corre- 
spond to  electric  potential  in  electromotive  force  measure- 
ments. These  electric  potentials  are  not  as  yet  susceptible 
to  quantitative  measurement  in  the  same  way  as  the  electro- 
motive forces  in  galvanic  cells,  but  the  principle  is  similar 
and  the  chemical  affinity  of  a  given  combination  may  be 
expressed  as  electromotive  force  or  electric  potential,  or 
more  in  conformity  with  the  valence  views  used,  an  electron 
potential.  This  electron  potential  of  an  atom  in  combina- 
tion will  manifestly  be  different  in  different  compounds, 
just  as  the  electromotive  force  of  an  element  is  different  in 
different  combinations  of  solvent,  etc.  The  electron  poten- 
tial cannot  be  measured  quantitatively  at  present  as  already 
stated  except  in  isolated  cases,  but  it  can  be  used  in  a 
qualitative  sense  in  a  classification  of  reactions.  Recalling 
the  definition  of  oxidation  and  reduction,  it  is  plain  that 
for  electron  potential  when  used  to  compare  different  sub- 
stances, may  be  substituted  relative  oxidizing  and  reducing 
potentials,  or  what  amounts  to  the  same  thing,  the  affinity 
of  the  element  for  the  electron  under  the  given  conditions. 
The  theoretical  developments  outlined  apply  to  all  chem- 
ical compounds  and  reactions.  The  next  step  will  be  to 
study  the  distribution  of  the  valence  electrons  in  a  molecule, 
or  the  valences  of  the  different  atoms  in  a  molecule.  A 
clear  understanding  of  these  valences  (positive  or  negative) 
is  necessary  for  the  formulation  of  compounds  on  the  basis 
of  the  electron  conception  of  valence,  just  as  fifty  years 
ago  the  arrangement  of  atoms  in  a  molecule  and  their 


OXIDATION-REDUCTION.  171 

linkings  formed  one  of  the  outstanding  problems  in  chem- 
istry. The  reactions  of  the  various  substances  preferably 
with  simple  reagents  at  that  time  formed  the  basis  for  the 
elucidation  of  the  structures,  the  valences  of  the  atoms 
then  forming  the  general  underlying  groundwork  for  further 
developments.  The  combined  study  of  the  valences  and 
the  reactions  together  with  the  underlying  principles  re- 
sulted in  the  great  growth  of  structural  chemistry. 

The  same  general  method  must  now  be  used  in  the  newer 
developments  of  chemical  structures  involving  the  electron 
conception  of  valence.  On  the  basis  of  previous  knowledge 
and  some  fundamental  assumptions  (as  few  as  possible) 
definite  rules  of  electron  linkings  may  be  developed.  These 
will  then  be  used  in  connection  with  certain  simple  chemical 
reactions,  and  the  structures  modified  when  necessary. 
In  this  way  by  correlating  the  relations  found  by  these 
methods,  certain  rules  for  indicating  structures  will  be 
developed  and  then  applied  to  classifying  reactions.  The 
knowledge  of  the  exact  distribution  of  the  valence  electrons 
was  not  absolutely  essential  to  the  reactions  discussed  in 
the  preceding  chapters  as  long  as  there  was  no  change  in 
this  distribution  involving  oxidation  and  reduction.  Since 
oxidation  and  reduction  reactions  involve  the  change  in 
electric  charge  of  certain  atoms,  a  knowledge,  as  complete 
as  possible  under  the  conditions,  of  the  initial  states  of 
oxidation  of  the  atoms  reacting,  is  essential.  The  remainder 
of  this  chapter  will  be  devoted  to  a  review  of  some  of  the 
principles  of  use  in  the  determination  of  the  electron  struc- 
tures, and  in  the  following  chapter  will  be  presented  a 
number  of  oxidation-reduction  reactions  using  the  structures 
developed. 

In  the  first  chapter,  some  of  the  fundamental  principles 
upon  which  the  electronic  structures  of  compounds  may  be 
based  were  outlined.  Thus,  the  older  ideas  of  positive 
and  negative  atoms  and  groups  were  shown  to  have  attained 


172  CHEMICAL  REACTIONS. 

a  definite  and  precise  meaning  with  the  electron  conception 
of  valence.  The  experimental  determinations  of  trans- 
ference numbers  and  conductances  of  ionized  substances 
were  shown  to  be  a  direct  method  for  finding  some  of  the 
charges  on  some  of  the  atoms  or  groups.  The  arrangement 
of  the  elements  in  the  Periodic  System  of  Mendeleeff  is,  in 
part,  an  expression  of  the  differences  in  the  properties  under 
discussion,  and  probably  serves  as  the  most  general  method 
for  indicating  the  relative  oxidation  potentials  of  the  differ- 
ent elements  under  ordinary  conditions.  The  atom  of  an 
element  of  high  oxidizing  potential  would,  in  forming  a 
chemical  linking,  receive  a  negative  electron  from  an  atom 
of  an^element  of  low  oxidizing  potential,  or,  in  other  words, 
elements  of  high  oxidizing  potentials  are  ordinarily  negative 
toward  elements  of  low  oxidizing  potentials.  The  arrange- 
ment of  the  elements  in  the  Periodic  System  brings  out 
regularities  such  as  the  relative  positive  and  negative 
properties  of  the  elements.  In  the  horizontal  rows,  the 
elements  of  larger  atomic  weights  are  negative  toward 
those  of  smaller,  receive  electrons  to  form  chemical  linkings, 
possess  higher  oxidation  potentials;  in  the  vertical  rows, 
the  elements  of  smaller  atomic  weights  receive  negative 
electrons  from  those  of  larger  atomic  weights  in  forming 
chemical  linkings. 

These  regularities  apply  however  only  to  the  stable  forms 
of  chemical  linkings.  It  is  readily  conceivable  that  under 
special  conditions  compounds  will  be  formed  in  which  the 
linking  is  less  stable  and  in  which  the  negative  electron  is 
transferred  in  the  direction  opposite  to  that  of  the  stable 
linking.  This  would  be  the  case  with  elements  whose 
oxidation  potentials,  or  affinity  for  negative  electrons,  do 
not  differ  widely,  or  with  elements  with  great  inertia  whose 
velocity  of  reaction  is  slow  so  that  they  would  exist  for  a 
measurable  time  in  unstable  forms  of  combination.  These 
questions  will  be  taken  up  again. 


OXIDATION-REDUCTION.  173 

In  order  to  determine  the  structural  formulas  of  sub- 
stances, physical  or  chemical  methods  or  both  simultane- 
ously may  be  used.  The  use  of  a  physical  method  will 
now  be  given  in  some  detail.  The  linking  of  carbon  with 
carbon,  in  which  partly  owing  to  inertia  to  reaction,  the 
states  of  oxidation  of  the  carbon  atoms  cannot  be  deter- 
mined readily,  is  involved  in  these  structures  (cf.  K.  G. 
Falk,  Jour.  Amer.  Chem.  Soc.  33,  1140  (1911)). 

The  structures  of  organic  acids  as  deduced  from  their 
ionization  constants  in  aqueous  solutions  will  be  developed. 
The  ionization  constants  (K  X  105)  of  the  acids  as  calcu- 
lated from  the  Ostwald  dilution  law, 


.(1-7)' 

in  which  v  =  the  volume  in  cubic  centimeters  containing 
one  mol  of  the  acid,  and  7  =  the  degree  of  ionization  found 
from  the  conductance  ratio,  will  be  used.  Only  those  acids 
will  be  considered  for  which  a  fairly  reliable  value  of  K  has 
been  obtained.  This  eliminates  the  highly  ionized  acids 
for  which  K  varies  with  change  in  concentration.  The 
data  refer  to  25°. 

In  considering  the  structures  of  the  organic  acids,  it  is 
evident  that  the  a-carbon  atom  (the  one  combined  directly 
with  the  carboxyl  group)  influences  the  ionization  constant 
of  the  acid  to  the  greatest  extent.  A  classification  of  the 
acids  will  be  given  which  depends  upon  the  direction  of  the 
valences  by  which  this  a-carbon  atom  is  combined  with  the 
other  atoms  in  the  molecule,  or  its  valence,  or  its  oxidation 
potential.  This  divides  the  acids  into  four  general  classes 
which  may  be  formulated  as  follows: 

I  ^C.C02H;  II  ^C.C02H;  III  ^C.C02H;  IV  ^C.C02H. 

The  carboxyl  group  is  assumed  to  be  negative  to  the  a- 
carbon  atom  and  to  exert  practically  the  same  effect  on  the 


174  CHEMICAL  REACTIONS. 

valence  throughout.  The  acids  belonging  to  class  I  are 
those  in  which  three  electropositive  groups  are  combined 
with  the  a-carbon  atom;  those  belonging  to  class  II,  two 
electropositive  and  one  electronegative;  to  class  III,  one 
electropositive  and  two  electronegative.  The  ionization 
constants  are  found  to  increase  in  the  order  of  the  classes 
I,  II,  III,  IV.  The  acids  represented  by  formula  IV,  such 
as  trichloracetic  acid,  are  too  highly  ionized  to  give  satis- 
factory dissociation  constants,  and  will  not  be  considered 
here. 

This  method  of  consideration  differs  from  the  ordinary 
one,  which  attributes  the  variation  of  the  ionization  con- 
stant directly  to  the  nature  of  the  neighboring  atoms  or 
groups,  in  assuming  that  the  influences  determining  the 
magnitude  of  the  ionization  constant  are  the  positions  of 
the  electric  charges  on  the  atoms.  These  positions  indeed 
are  determined  by  the  nature  of  the  adjacent  atoms  or 
groups,  so  that  the  new  view  is  to  be  regarded  as  a  develop- 
ment of  the  older  idea,  which  serves  to  give  it  greater 
definiteness.  The  influences  exerted  by  the  double  or 
triple  bond,  according  to  the  newer  point  of  view,  are 
made  up  additively  of  the  influences  exerted  by  the  two  or 
three  single  bonds  or  valences.  The  groups  combined  with 
the  j3-carbon  atom,  or  the  directions  of  the  valences  of  this 
atom,  doubtless  influence  the  ionization  constant;  but  as 
will  be  seen,  this  influence  is  in  most  cases  of  small  im- 
portance when  compared  with  the  influence  exerted  by  the 
bonds  of  the  a-carbon  atom.  The  groups  combined  in  the 
7,  d,  etc.,  positions  doubtless  exert  an  influence  on  the 
constants  also,  but  this  influence  is  negligible  in  the  con- 
sideration of  this  classification. 

Although  the  classification  depends  primarily  upon  the 
directions  of  the  valences,  the  specific  effect  of  certain 
groupings  may  be  great  enough  at  times  to  exert  a  pre- 
dominating influence  and  obscure  the  relations  mentioned. 


OXIDATION-REDUCTION.  175 

These  effects,  which  are  unquestionably  present  with  every 
atom  or  group  in  an  acid,  are  too  small  to  be  perceived  with 
the  present  methods  of  experiment  and  calculation  and 
therefore  do  not  interfere  when  the  acids  are  divided  into 
the  general  classes  depending  upon  the  directions  of  the 
valences  of  the  a-carbon  atom  except,  possibly,  in  individual 
cases.  Acids  which  contain  an  amino  group  will  not  be 
included  in  the  discussion,  and  all  acids  containing  sulfur 
will  be  omitted  as  well. 

Saturated  Monobasic  Acids. — In  the  aliphatic  acids  con- 
taining only  carbon  and  hydrogen  in  combination  with  the 
carboxyl  group,  the  arrangement  of  the  bonds  of  the  a- 
carbon  atom  may  as  stated  be  represented  by  the  formula 
^C.CC^H.  The  values  of  the  ionization  constant  for  these 
acids  vary  between  0.0011  and  0.0020  and  include  the  follow- 
ing, arranged  in  the  order  of  increasing  values  for  the 
constant:  pelargonic,  caprylic,  caproic,  isobutyric,  heptylic, 
isocaproic,  butyric,  valeric,  ethylmethylacetic,  isovaleric, 
acetic,  tetramethylenecarboxylic,  and  diethylacetic.  The 
following  acids  and  their  dissociation  constants  contain  the 
same  bonds  for  the  ce-carbon  atom  as  the  acids  just  con- 
sidered, but  are  substituted  by  halogens,  hydroxyl  groups, 
phenyl  groups,  etc.,  in  the  /?-,  7-,  or  ^-positions:  d-chlor- 
valeric,  0.0020;  benzoylpropionic,  0.0022;  hydrocinnamic, 
0.0023;  levulinic,  0.0026;  /3-hydroxypropionic,  0.0031;  0- 
chlorpropionic,  0.0086;  0-chlorbutyric,  0.0089;  /3-iodbuty- 
ric,  0.0090;  /3-brompropionic,  0.0098;  and  eleven  substi- 
tuted j3-hydroxypropionic  acids,  0.0015  to  0.0045.  To 
these  may  be  added  phenylacetic,  0.0056,  and  hydroatropic, 
0.0043,  indicating  that  the  phenyl  group  as  a  substituent 
exerts  an  influence  on  the  ionization  constants  of  acids 
similar  to  that  exerted  by  the  methyl,  etc.,  groups.  The 
ionization  constants  for  these  acids  are  less  than  0.005 
except  for  the  three  /3-halogen  propionic  and  phenylacetic 
acids,  and  for  these  they  are  less  than  0.01.  The  constitu- 


176  CHEMICAL  REACTIONS. 

tive  effect  is  evident  here,  but  is  it  not  great  enough  to 
mask  the  additive  influence  of  the  bonds  (as  will  be  seen 
presently  with  the  a-halogen  substituted  acids).  For  the 
acids  containing  the  grouping  ^C  —  C02H,  the  constant 
may  be  taken  in  general  to  lie  between  0.001  and  0.005  with 
variations  due  to  the  constitutive  effect  of  the  substituting 
groups  up  to  0.01  and  possibly  higher. 

(The  data  for  the  acids  refer  to  25  degrees  and  were 
taken  from  the  results  of  the  following  observers:  W.  Ost- 
wald,  Z.  physik.  Chem.  3,  170,  241,  369  (1889);  H.  G. 
Bethmann,  Ibid.,  5,  385  (1890);  M.  Berthelot,  Ann.  chim. 
phys.,  (6),  23,  43  (1891);  A.  Crum  Brown  and  J.  Walker, 
Lieb.  Ann.,  261,  116  (1891);  J.  Walker,  Trans.  Chem.  Soc., 
61,  696  (1892);  P.  Walden,  Z.  physik.  Chem.,  8,  433  (1891); 
10,  646  (1892);  F.  Stohmann  and  C.  Kleber,  J.  prakt. 
Chem.,  45,  475  (1892);  A.  Hantzsch  and  A.  Miolati,  Z. 
physik.  Chem.,  10,  23  (1892);  E.  Franke,  Ibid.,  16,  482 
(1895);  H.  Euler,  Ibid.,  21,  264  (1896);  B.  Szyszkowski, 
Ibid.,  22,  173  (1897);  W.  A.  Smith,  Ibid.,  25,  194  (1898); 
W.  A.  Bone  and  C.  H.  G.  Sprankling,  Trans.  Chem.  Soc., 
77,  654  (1900);  D.  M.  Lichty,  Lieb.  Ann.,  319,  369  (1901); 
W.  A.  Bone,  J.  J.  Sudborough  and  C.  H.  G.  Sprankling, 
Trans.  Chem.  Soc.,  85,  534  (1904);  K.  Drucker,  Z.  Physik. 
Chem.,  #2,642  (1905).) 

The  formula  for  the  aliphatic  acids  containing  a  halogen 
or  similar  (negative)  substituent  in  the  ce-position  may  be 
represented  by  ^C  —  CO2H.  The  acids  belonging  to  this 
class  which  have  been  studied  are  iodacetic,  0.075;  a- 
brombutyric,  0.106;  a-brompropionic,  0.108;  bromacetic, 
0.138;  «-chlorbutyric,  0.139;  a-chlorpropionic,  0.147; 
chloracetic,  0.155;  sulfocyanacetic,  0.265;  cyanacetic, 
0.370;  and  a,  /3-dibrompropionic,  0.67.  For  acids  of  this 
class,  the  constant  may  be  taken  as  lying  between  0.1  and 
0.4  unless  modified  very  markedly  by  some  constitutive 
influence. 


OXIDATION-REDUCTION.  177 

Few  acids  containing  two  negative  substituents  in  the 
a-position  of  the  formula  ^C  —  CO2H  have  been  studied. 
a,  a-Dibrompropionic,  3.3,  and  dichloracetic,  5.2,  are  the 
only  ones  for  which  data  were  found.  Acids  containing 
three  negative  substituents  in  the  a-position  are  too  highly 
ionized  for  the  purpose  in  view  and  do  not  give  a  satisfactory 
constant. 

The  constants  for  the  acids  so  far  considered  may  be 
summarized  as  follows:  For  the  grouping  j^C  —  C02H,  less 

than  0.01;  for  ^C  -  CO2H,  0.1  to  0.4;  for  ^C  -  CO2H, 
greater  than  2.  Individual  substituents  modify  these 
values  to  a  greater  or  less  extent,  but  the  differences  be- 
tween the  three  classes  appear  to  be  great  enough  to 
enable  a  decision  to  be  reached  as  to  the  structure  of  a 
given  acid  in  most  cases. 

A  group  of  acids  for  which  the  constants  lie  between 
those  for  the  acids  containing  the  groupings  ^C  —  CC^H 

and  ^C  —  CC^H  is  known.  This  group  comprises  the 
acids  diisopropylglycollic,  0.013;  lactic,  0.014;  gly collie, 
0.015;  glyceric,  0.023;  ethoxyacetic,  0.023;  methoxyacetic, 
0.034;  mandelic,  0.042;  phenoxyacetic,  0.076;  andbenzilic, 
0.092.  The  OR  (R  =  H  or  hydrocarbon  radical)  is  evi- 
dently the  reason  why  these  acids  occupy  an  intermediate 
position  between  the  acids  containing  no  negative  a-group 
and  those  containing  one.  This  OR  group  is  generally 
taken  to  have  an  effect  similar  to  a  negative  group,  and 
would  therefore  be  formulated  — >OR  in  the  acids.  Some 
of  the  acids  approach  the  values  for  acids  of  the  class 
^C  —  C02H,  but  for  most  of  them  the  difference  is  so 
large  that  it  must  be  assumed  that  either  the  OR  group 
exerts  a  constitutive  influence  masking  to  a  great  extent 
the  effect  of  the  bonds  or  that  there  is  some  action  (such  as 
inner  oxonium  salt  formation,  similar  to  that  taking  place 
with  amino  acids)  between  the  ether  or  hydroxyl  oxygen 


178  CHEMICAL  REACTIONS. 

and  the  hydrogen  or  other  part  of  the  carboxyl  group  which 
decreases  the  values  of  K  for  this  group  of  acids  as  com- 
pared with  the  acids  containing  a  different  negative  substi- 
tuent  in  the  a-position,  resulting  in  a  constant  of  from  0.01 
to  0.1.  It  may  be  pointed  out,  however,  that  the  class  to 
which  any  given  acid  belongs  may  readily  be  ascertained 
as  the  composition  taken  in  connection  with  the  dissociation 
constant  shows  the  structure  of  the  a-carbon  atom.  An 
acid  such  as  trichlorlactic,  0.465,  must  be  formulated 
somewhat  differently  and  probably  is  best  represented  by 


the  structure  HO  ^—  C  —  COH  or  intermediate  between  the 


I^C  —  C02H  and  ^C  —  C02H  classes,  just  as  lactic  acid 
is  intermediate  between  the  ^C  -  C02H  and  ^C  -  C02H 
classes. 

Saturated  Dibasic  Acids.  —  W.  Ostwald  was  the  first  to 
point  out  that  the  constants  obtained  by  his  dilution  law 
for  the  organic  dibasic  acids  referred  to  the  first  hydrogen 
ion  which  was  formed  from  the  acid  and  that  the  second 
hydrogen  ionizes  only  in  very  dilute  solutions,  so  that  it 
does  not  enter  into  the  constant  as  ordinarily  determined. 
For  some  acids  the  second  hydrogen  begins  to  ionize  appre- 
ciably at  a  dilution  of  about  500  liters,  but  the  constant  as 
determined  experimentally  in  the  usual  way  is  found  to 
increase  rapidly  with  the  dilution  when  this  occurs.  A 
study  of  the  constants  for  the  dibasic  acids  may  therefore 
follow  the  lines  laid  down  for  the  monobasic  acids  by  con- 
sidering the  carboxyl  group  containing  the  un-ionized 
hydrogen  as  a  negative  substituent. 

Malonic  acid,  from  this  point  of  view,  is  carboxyl  acetic 
acid,  and  should  belong  to  the  ^C  —  C02H  class.  Its 
constant  is  found  to  be  0.164.  The  following  substituted 
malonic  acids,  with  their  ionization  constants,  have  been 
measured:  dimethylmalonic,  0.076;  a,  a-tetramethylenedi- 


OXIDATION-REDUCTION.  179 

carboxylic,  0.080;  isobutylmalonic,  0.090;  octylmalonic, 
0.095;  heptylmalonic,  0.102;  butylmalonic,  0.103;  propyl- 
malonie,  0.112;  hexamethylenetetracarboxylic  (1,  1,  3,  3), 
0.12;  isopropylmalonic,  0.127;  ethylmalonic,  0.127;  benzyl- 
malonic,  0.151;  allylmalonic,  0.154;  ethylmethylmalonic, 
0.164;  /3-benzoylisosuccinic,  0.250;  methylbenzylmalonic, 
0.266.  These  acids  evidently  all  belong  to  the  class 
^C  -  C02H. 

Two  substituted  malonic  acids  have  been  measured 
which  doubtless  belong  to  the  ^C  —  C02H  class;  chlor- 
malonic,  4,  and  a,  a-trimethylenedicarboxylic,  2.1. 

Succinic  acid  may  be  represented  by  the  formula 

(a=)H02C  -  CH2  ->  CH2  -  CO2H(/3). 

If  the  a-hydrogen  is  ionized  more  easily  than  the  /?,  succinic 
acid  should  belong  to  the  ^C  —  C02H  class;  if  the  0 

more  easily  than  the  a,  to  the  ^C  —  C02H  class.  A 
study  of  the  constants  for  succinic  acid  and  the  acids 
derived  from  it,  in  which  a  hydrogen  atom  of  one  of  the 
methylene  groups  is  replaced  by  hydrocarbon  radicals 
shows  that  the  acids  belong  to  the  ^C  —  C02H  class 
(analogous  to  acetic  acid),  the  negative  carboxyl  substituent 
in  the  /3-position  exerting  a  constitutive  effect  similar  to 
that  exerted  by  the  halogens  in  the  ^-substituted  propionic 
acids.  The  results  for  these  acids  are  as  follows:  Succinic, 
0.0068;  isopropylsuccinic,  0.0075;  asym.  dimethylsuccinic, 
0.0081;  methylsuccinic,  0.0085;  ethylsuccinic,  0.0086; 
isobutylsuccinic,  0.0088;  propylsuccinic,  0.0089;  benzyl- 
succinic,  0.0091  ;  and  allylsuccinic,  0.0109.  The  three  acids, 
bromsuccinic  0.278,  chlorsuccinic  0.284,  and  sym.  brom- 
methylsuccinic  0.478,  evidently  belong  to  the  ^C  —  CC^H 
class  analogous  to  chloracetic  acid  and  must  be  formulated 


(for  the  first  named  as  example)  Clx^  |  ?  in  which 


180  CHEMICAL  REACTIONS. 

each  of  the  carbon  atoms  combined  with  a  carboxyl  has 
gained  two  and  lost  one  negative  electron. 

The  higher  homologs  of  the  saturated  dibasic  acids  may 
be  considered  as  derived  from  the  higher  fatty  acids  con- 
taining a  negative  substituent  which  exerts  only  a  minor 
influence  upon  the  ionization  constants  as  compared  with 
the  effect  of  the  bonds.  They  should  therefore  belong  to 
the  i^C  —  C02H  class,  and,  in  fact,  the  constants  for  those 
measured  are  found  to  lie  between  0.0022  and  0.0059.  The 
following  acids  are  included  and  are  arranged  in  the  order 
of  increasing  values  for  K:  Camphoric,  sebasic,  azelaic, 
suberic,  co,  co'-dipropylpimelic,  co,  o/-diisopropylpimelic,  n- 
pimelic,  o>,  co'-dimethylpimelic,  w,  o/-diethylpimelic,  adipic, 
glutaric,  co,  co'-dibenzylpimelic,  a-methylglutaric,  a,  a'- 
diethylglutaric,  |S,  /3'-dimethylglutaric,  a,  a'-dimethylglu- 
taric,  and  /3-methylglutaric. 

Unsaturated  Acids. — The  unsaturated  acids  will  be  taken 
up  in  the  same  way  as  the  saturated,  and  the  double  bond 
will  be  assumed  to  have  the  same  effect  upon  the  dissocia- 
tion constant  as  if  it  were  made  up  of  two  single  bonds. 
It  will  be  seen  that  a  perfectly  rational  classification  follows 
from  this  method  of  treatment  and  that  the  acids  containing 
a  double  bond  between  two  carbon  atoms  fall  into  the  same 
groups  depending  upon  the  directions  of  the  valences  and 
considering  their  influence  as  purely  additive,  as  the 
saturated  acids.  Caution  must  be  used  however  with 
regard  to  the  data  for  some  of  the  isomeric  acids,  as  the 
methods  of  isolating  the  pure  substances  had  not  been 
worked  out  very  satisfactorily  when  some  of  the  measure- 
ments were  made.  The  following  monobasic  acids  contain- 
ing a  double  bond  between  the  a-  and  0-carbon  atoms  in 
four  cases  and  between  the  j3-  and  7-  in  one  case  may  first 
be  quoted:  Methylethylacrylic,  0.0011;  sorbic,  0.0017; 
hydrosorbic,  0.0024;  trimethylacrylic,  0.0039;  and  acrylic, 
0.0056.  These  acids  evidently  belong  to  the  ^C  - 


OXIDATION-REDUCTION.  181 

class,  whether  the  a-carbon  atom  is  combined  with  the 
other  atoms  in  the  molecule  by  means  of  three  single  bonds 
or  one  double  bond  and  one  single  bond. 

In  the  case  of  the  isomeric  unsaturated  acids,  maleic  and 
f  umaric  acids  may  be  considered  in  some  detail,  since  these 
substances  were  isolated  in  a  state  of  purity  early  and 
the  measurements  for  finding  the  values  of  K  may  be  con- 
sidered to  be  accurate.  Furthermore,  the  composition  of 
the  two  acids  is  simple  and  it  should  be  possible  to  draw 
perfectly  definite  conclusions.  The  ionization  constant  of 
fumaric  acid  was  found  to  be  0.093,  and  that  of  maleic 
acid  1.17.  The  possible  structures  for  these  acids  are 
(a)  C02H.CH  ^  CH.CO2H  and  (6)  CO2H.CH  :£  CH.CO2H. 
Since  the  ionization  constants  refer  to  one  hydrogen  ion 
and  the  carboxyl  group  may  be  considered  as  a  negative 
substituent,  fumaric  acid  from  the  value  of  its  constant 
should  belong  to  the  ^C  —  C02H  class  and  must  be  as- 
signed formula  (a).  Maleic  acid  should  then  be  repres- 
ented by  formula  (6)  .  An  acid  of  this  formula  can  ionize 
in  one  of  two  ways,  either  from  the  ^C  —  CO2H  group  or 

from  the  ^C  —  C02H  group.  The  ionization  constants 
for  the  acids  belonging  to  these  classes  differ  widely,  and 
the  value  found  for  maleic  acid,  1.17,  shows  that  the  ioniza- 
tion takes  place  by  the  first  of  the  methods  indicated  .  Maleic 
acid  may  then  be  classed  with  dichloracetic  acid,  and  fumaric 
acid  with  monochloracetic  acid  in  considering  the  ionization 
of  the  first  hydrogen. 

The  acids  containing  a  triple  bond  can  be  disposed 
of  briefly,  as  few  have  been  measured.  Tetrolic  acid, 
0.246,  is  to  be  represented  by  the  formula  CH3^C.C02H, 
and  phenylpropiolic  acid,  0.59,  by  the  similar  formula 


Aromatic  Acids.  —  The  aromatic  acids  are  taken  to  include 
those  in  which  a  carboxyl  group  from  which  the  hydrogen 


182  CHEMICAL  REACTIONS. 

is  ionized  is  in  direct  combination  with  a  carbom  atom  of  the 
benzene  nucleus.  This  carbon  atom  corresponds  to  the 
a-carbon  atom  in  the  saturated  acids,  and  the  bonds  of  this 
carbon  atom  are  the  ones  which  determine  the  ionization 
constant  of  the  acid  in  question.  It  may  be  expected  that  a 
greater  constitutive  effect  is  exerted  by  the  benzene  ring 
on  the  constants.  This  is  true  to  a  certain  extent  as  the 
general  arrangement  (or  directions)  of  the  valences  and 
their  influence  upon  each  other  between  the  carbon  atoms 
in  the  ring  are  not  known,  but  the  aromatic  acids  may  be 
grouped  in  the  same  way  as  the  aliphatic  acids  and  the 
probable  reciprocal  influences  of  the  bonds  discussed  with- 
out specifying  the  particular  directions  of  all  the  valences. 
In  general  terms,  the  benzene  ring  is  assumed  to  contain 
alternate  single  and  double  bonds. 

The  ionization  constant  for  benzoic  acid  was  found  to 
be  0.0067.  This  indicates  that  benzoic  acid  belongs  to  the 
^C  —  CC^H  class,  and  that  its  graphic  formula  is 

C02H 

H—  C  —  C*=C^— H 

II  I 

H— -  C —  C=C« — H 

H 

the  direction  of  the  bonds  indicated  by  dashes  being  un- 
known. Other  aromatic  acids  in  which  the  directions  of  the 
valences  for  carbon  (1)  are  the  same  as  for  benzoic  acid,  but 
for  which  the  arrangement  of  the  other  bonds  is  unknown 
except  that  no  strong  constitutive  effect  is  manifested  by 
the  two  carbon  atoms  in  position  (2)  and  that  therefore  the 
directions  of  the  bonds  in  these  are  not  such  as  would  be 
expected  if  only  negative  groups  were  combined  with  them, 
are  the  following:  p-Hydroxybenzoic,  0.0029;  vanillic, 
0.0030;  iso vanillic,  0.0032;  anisic,  0.0032;  veratric,  0.0036; 
mesitylenic,  0.0048;  m-toluic,  0.0051;  p-toluic,  0.0052; 


OXIDATION-REDUCTION.  183 

methylsalicylic,  0.0082;  m-hydroxybenzoic,  0.0083;  1,  3, 
5-dihydroxybenzoic,  0.0091;  and  p-chlorbenzoic,  0.0093. 

The  following  acids  may  be  assigned  to  the  same  class 
as  benzoic  acid;  m-fluorbenzoic,  0.0136;  m-brombenzoic, 
0.0137;  m-chlorbenzoic,  0.0155;  m-iodbenzoic,  0.0163;  m- 
cyanbenzoic,  0.0199;  isophthalic,  0.0287;  m-nitrobenzoic, 
0.0345;  o-toluic,  0.0120;  p-nitrobenzoic,  0.0396;  and  1,  2, 
4-resorcylic,  0.0515.  In  the  first  seven  of  these  acids,  the 
negative  substituent  in  position  (3)  (or  corresponding  to 
the  7-position  in  the  aliphatic  acids)  apparently  exerts  a 
constitutive  effect  on  the  constant  comparable  with  some 
of  the  effects  exerted  by  negative  constituents  in  the  /?- 
position  of  the  aliphatic  acids.  This  effect  may  be  due 
to  the  influence  of  the  negative  constituents  on  the  direction 
of  the  valences  between  the  carbon  atoms  (2)  and  (3), 
causing  the  valences  for  (2)  to  assume  directions,  which,  if 
present  in  aliphatic  acids,  would  cause  similar  changes  in 
the  constants.  Similar  reasoning  may  be  applied  to  the 
last  three  acids. 

The  following  acids  must  be  assigned  to  the  ^C.C02H 
class,  and  the  probable  structure  of  part  of  the  molecule 

C02H 

may  be  formulated  as  c  _  ^  Q     >  c  :  salicylic,  0.102;  1,2, 

•  •  •  • 

5-hydroxy salicylic,  0.108;  1,  2,  3-hydroxy salicylic,  0.114; 
o-phthalic,  0.121  ;  o-chlorbenzoic,  0.132  ;  o-brombenzoic, 
0.145;  m,  m-dinitrobenzoic,  0.162;  and  o-nitrobenzoic,  0.616. 

The  only  acid  which  appears  to  belong  to  the  ^C.COzH 
class  is  1,  2,  6-resorcylic,  5.0. 

These  results  show  a  method  for  finding  the  directions 
of  the  valences  or  the  distribution  of  some  of  the  valence 
electrons  on  the  carbon  atoms  of  the  benzene  ring,  and  the 
possibilities  of  rearrangement  of  these  electrons  when 
different  groups  are  substituted  for  the  hydrogens  of  the 
benzene. 
13 


184  CHEMICAL  REACTIONS. 

Chemical  methods  can  also  be  used  to  determine  the  dis- 
tribution of  the  charges  in  a  molecule,  or  the  valence  of  the 
atoms  and  should  prove  of  more  general  applicability. 
Although  no  one  reaction  can  be  chosen  as  an  infallible 
guide,  the  reaction  which  can  be  relied  upon  most  frequently 
is  that  involving  hydrolysis  (cf.  T.  Selivanow,  Ber.  25,  3617 
(1892);  W.  A.  Noyes,  Jour.  Chem.  Amer.  Soc.  3d,  769 
(1913);  etc.).  In  this  reaction,  when  an  atom  or  group  is 
replaced  by  a  hydrogen  atom  or  hydroxyl  group  derived 
from  water,  unless  there  is  very  distinct  evidence  to  the 
contrary,  it  may  be  assumed  that  no  change  in  the  electrical 
states  of  the  atoms  taking  part  in  the  reaction  occurs.  If 
acid  or  base  is  present  and  accelerates  the  hydrolysis, 
there  may  be  a  greater  possibility  of  electrical  change,  but 
still  unless  there  is  evidence  to  the  contrary,  no  change  may 
also  be  assumed  here.  With  substances  containing  single 
bonds  only,  the  oxidation  potentials  of  the  atoms  should  as 
a  rule  be  so  different  that  only  one  form  of  the  substance 
is  stable. 

With  compounds  containing  a  double  bond,  the  conditions 
are  not  so  simple,  however.  It  is  necessary  to  consider  all 
the  possible  cases  and  from  a  study  of  the  reactions  decide 
which  formula  may  be  assigned  to  a  given  compound. 
Taking  up  substances  which  contain  a  double  bond  between 
two  carbon  atoms  first,  it  is  evident  that  these  compounds 
may  in  general  be  divided  into  classes:  (1)  compounds  in 
which  the  two  halves  of  the  molecule  are  similar;  and  (2) 
compounds  in  which  the  two  halves  of  the  molecule  are 
dissimilar.  To  the  first  class  belong  substances  of  the  types 

^  CRs;  CR*  ^  CR*;  CRR'  ^  CRR';  CRR'  It  CRR'. 


If  two  isomers  exist  in  any  case,  because  of  the  difference 
in  valence  of  the  carbon  atoms  or  their  oxidation  potentials, 
one  would  be  expected  to  be  more  stable  than  the  other;  if 
only  one  substance  of  the  general  type  exists,  then  it  may 


OXIDATION-REDUCTION.  185 

be  that  the  other  is  too  unstable  to  be  formed  permanently, 
going  over  into  the  stable  form,  and  it  would  be  a  question 
then  to  determine  by  means  of  the  chemical  reactions*  to 
which  of  the  two  types  its  reactions  show  it  to  conform 
best. 

Of  substances  derived  from  the  formula  CR2  :  CR2,  none 
is  known  to  exist  in  two  forms.  The  directions  of  the 
valences,  or  the  charges  of  the  atoms  in  the  compounds  of 
this  group  might  be  determined  by  following  some  of  the 
addition  reactions  of  closely  related  compounds.  Since 
the  molecule  is  symmetrical,  it  makes  no  difference  in  the 
resulting  compound,  in  which  way  another  substance,  HI 
for  instance,  is  added.  If  however,  as  a  typical  example, 
propylene  CHa.CH  :  CH2,  is  taken,  there  would  be  three 
possibilities;  MeCH  ^  CH2  and  MeCH  ^  CH2  or  MeCH 
tl  CH2.  On  treatment  with  HI,  if  either  of  the  last  two 
represents  the  structural  formula,  the  I  would  all  go  to  one 
carbon  atom,  and  the  H  to  the  other,  only  one  substance 
being  formed;  while  if  the  first  represents  the  structure, 
a  mixture  of  two  substances  should  be  formed,  the  H  and  I 
being  divided  between  the  two  carbon  atoms.  The  reac- 
tions in  this  case  might  be  represented  as  follows: 

MeCH  ^  CH2  =  MeCH2  -»  CH2I  and 

H-»I 

I  <-H 
MeCH  l^  CH2  =  MeCHI  <-  CH3. 

The  extent  to  which  each  of  the  products  would  be  formed 
would  depend  upon  the  influence  of  the  methyl  group  as 
compared  with  the  hydrogen  or  the  double  bond,  and  upon 
the  difference  in  polarity  between  the  hydrogen  and  iodine; 
the  smaller  the  difference  the  more  nearly  equal  would  be 
the  amounts  of  the  two  products  formed.  The  following 
results  were  obtained  by  A.  Michael  (J.  pr.  Chem.  60,  286, 
409  (1899)): 


186  CHEMICAL  REACTIONS. 

Propylene  +  HI  formed  principally  (CH3)2CHI  together 
with  a  little  C2H5CH2I. 

Propylene  +  ClBr  yielded  5  parts  CH3.CHBr.CH2Cl  to  7 
parts  CH3.CHCl.CH2Br. 

Propylene  +  C1I  yielded  1  part  CH3.CHI.CH2C1  to  4  parts 
CH3.CHC1.CH2I. 

Propylene  +  HOC1  formed  principally  CH3.CHOH.CH2C1 
and  perhaps  a  little  CH3.CHC1.CH2OH. 

These  examples  indicate  that  the  compounds  belong  to  the 
CR^CRs  type,  although  propylene  does  not  belong  to 
this  symmetrical  type.  In  general,  therefore,  if  one  form 
exists,  this  formula  is  assigned  to  it,  if  two  forms,  the  more 
stable  possesses  this  formula. 

Of  substances  derived  from  the  structure  CRR'  :  CRR' 
a  large  number  of  isomers  are  known,  of  which  maleic  and 
fumaric  acids  may  serve  as  examples.  From  what  has 
been  said,  the  more  stable,  fumaric  acid,  may  be  assigned 
the  formula  CRR' ^  CRR',  the  less  stable,  maleic  acid, 
the  formula  CRR' It  CRR'.  These  structures  agree  with 
the  structures  developed  from  the  ionization  constants  of 
acids. 

With  substances  containing  a  double  bond  in  which  the 
two  halves  of  the  molecule  are  dissimilar,  there  are  a  greater 
number  of  possibilities  with  three  possible  isomers  in  each 
case.  The  three  isomers  are  not  known  for  any  one  sub- 
stance with  certainty.  The  reason  for  this  may  be  found 
in  the  fact  that  if  the  two  halves  of  the  molecule  are  made 
up  of  groups  differing  very  much  in  properties,  of  the  two 
isomers  in  which  the  two  valences  act  in  the  same  direction, 
one  will  exhibit  very  much  greater  stability  than  the  other, 
making  it  extremely  difficult,  if  not  impossible,  to  isolate 
the  less  stable  form.  With  compounds  containing  a  double 
bond  between  two  unlike  atoms,  the  carbonyl  group  :  CO, 


OXIDATION-REDUCTION.  187 

for  example,  the  valences  assigned  may  be  indicated  as 
:  Cl£0,  since  the  properties  of  the  two  atoms  differ  so 
widely. 

It  must  be  pointed  out  that,  although  very  good  reasons 
exist  for  assigning  the  structures  indicated  to  the  various 
compounds  on  the  basis  of  chemical  reactions,  the  possi- 
bility remains  that  the  reagent  added  may  itself  cause  or 
influence  the  oxidation  potentials  of  the  reacting  atoms,  so 
that  the  structures  assigned  may  be  due  primarily  to  the 
reagent  used,  and  secondarily  to  the  structure  actually 
present  initially.  Although  this  possibility  does  not  appear 
to  apply  in  the  great  majority  of  cases,  it  must  be  pointed 
out  here,  as  unquestionably  it  does  occur  at  times. 

H.  S.  Fry,  some  years  ago  (Z.  physik.  Chem.  76,  387 
(1911);  cf.  also  L.  W.  Jones,  Jour.  Amer.  Chem.  Soc.  86, 
1268  (1914);  K.  G.  Falk  and  J.  M.  Nelson,  Science,  46,  551 
(1917)),  denoted  by  the  term  electromerism  the  phenomenon 
of  electronic  tautomerism,  including  substances  structurally 
identical,  but  mutually  transformable  by  an  exchange  of 
negative  electrons  between  the  atoms  composing  the  mole- 
cules. Thus,  ammonium  nitrate,  NH4NO3,  and  hydroxyl- 
amine  nitrite  NH3OHNO2,  while  mutually  transformable 
by  a  suitable  exchange  of  negative  electrons,  since  as  far 
as  the  charges  on  the  atoms  are  concerned  they  differ  only 
in  the  valence  or  state  of  oxidation  of  the  nitrate  and 
nitrite  nitrogen  atoms,  are  not  structurally  identical  and 
would  not,  therefore,  be  classed  as  electromers.  L.  W. 
Jones  applied  the  electromerism  view  to  a  number  of  com- 
pounds of  nitrogen  in  several  papers  published  recently. 

The  conception  of  electromerism  involves  the  isomerism 
of  maleic  and  fumaric  acids,  and  in  fact  all  isomerism 
heretofore  classed  under  cis-trans  or  geometrical  isomerism, 
without  considering  spatial  relationships  at  all.  Another 
group  of  substances  may  also  be  included  under  elec- 
tromerism. Werner  has  placed  in  parallel  the  so-called 


188  CHEMICAL  REACTIONS. 

geometrical  isomerism  of  double  bonded  carbon  atoms  and 
the  isomerism  due  to  plane  configuration  of  certain  cobalt, 
chromium,  and  platinum  compounds: 


X    X 
(Pt(NH3)2Cl2,  etc.) 

Whatever  explanation  is  accepted  for  the  double  bond 
isomerism,  the  same  explanation  will  apply  to  the  isomerism 
of  the  platinum  compounds.  Werner  considers  that  the 
explanation  of  the  spatial  configuration  applies  to  both. 
On  the  other  hand,  if  the  double  bond  isomerism  is  due 
to  the  directions  of  the  valences,  or  the  states  of  oxidation 
of  the  atoms,  or  the  distribution  of  the  negative  electrons, 
then  the  explanation  of  the  isomerism  of  the  platinum 
compounds  should  be  based  upon  the  distribution  of  the 
electrons  in  the  platinum  atom.  There  is,  however,  only 
one  atom  involved  here,  so  that  it  appears  as  if  this  isomer- 
ism would  furnish  a  method  for  showing  the  distribution  or 
arrangement  of  some  of  the  electrons  in  an  atom.  These 
platinum  and  similar  compounds  would  then  belong  to  the 
class  of  electromeric  substances.  Since  this  explanation 
means  that  the  spatial  arrangements  of  atoms  or  groups 
around  a  central  atom  depend  primarily  upon  the  spatial 
arrangement  of  the  valence  and  also  other  electrons  of  that 
central  atom,  a  further  logical  deduction  would  include  all 
optically  active  isomers  in  organic  and  inorganic  chemistry 
in  the  group  of  electromers.  The  spatial  arrangements  of 
of  the  atoms  or  groups  here  would  also  be  governed  or 
controlled  primarily  by  the  arrangement  of  the  electrons 
of  the  atom  showing  the  optical  activity. 

In  developing  the  structures  of  the  acids,  it  was  shown 
that  the  arrangements  of  the  valence  directions  in  the 
benzene  nucleus  were  different  in  different  acids,  or,  in 
other  words,  that  the  substituting  group  influenced  the 


OXIDATION-REDUCTION.  189 

valence  electrons  of  the  carbon  atoms  of  the  benzene 
nucleus.  The  states  of  oxidation  of  these  atoms  were 
different  depending  upon  the  substituting  group.  The 
benzene  nucleus,  therefore,  in  different  compounds  contain- 
ing various  substituents  acts  as  an  electromeric  substance, 
and  a  number  of  reactions  of  benzene  derivatives  will  un- 
doubtedly be  explained  upon  some  such  basis. 

Considering  the  states  of  oxidation  of  the  carbon  atoms 
of  the  benzene  ring  as  changed  and  basing  explanations 
of  reactions  upon  them  seems  more  logical  than  the  pro- 
cedure of  H.  S.  Fry,  who  more  or  less  arbitrarily  considers 
hydrogen  and  chlorine  to  be  either  positive  or  negative 
when  combined  with  the  benzene  nucleus,  and  then  bases 
explanations  of  substituting  and  other  reactions  upon  these. 
While  the  explanations  of  Fry  and  of  those  using  the  different 
charges  on  the  hydrogen  atoms  may  for  the  case  of  benzene 
amount  to  the  same  thing  and  one  view  be  no  more  advanta- 
geous than  the  other,  in  studying  chemical  reactions  in  gen- 
eral and  building  up  a  logical  consistent  system  of  chemical 
theory,  it  seems  better  to  treat  of  the  hydrogen  combined 
with  carbon  as  positive  until  direct  evidence  to  the  con- 
trary is  at  hand,  and  to  assign  the  changes  in  charges  in 
benzene  derivatives  to  the  carbon  atoms. 


CHAPTER  X. 

SOME  OXIDATION-REDUCTION  REACTIONS. 

The  structures  which  have  been  developed  in  the  last 
chapter  with  special  reference  to  the  states  of  oxidation  of 
various  atoms  in  molecules  will  now  be  applied  to  a  number 
of  reactions.  As  in  the  other  classifications  given  in  this 
book,  emphasis  is  placed  on  the  fact  that  the  same  principles 
apply  to  both  organic  and  inorganic  reactions  and  that  any 
reaction  in  one  branch  of  chemistry  can  be  paralleled  by  a 
reaction  in  the  other  branch.  In  oxidation-reduction  re- 
actions, certain  simple  principles  may  first  be  poirted  out. 
In  these  reactions,  when  an  oxidation  takes  place,  it  is 
always  a  particular  atom  which  is  oxidized.  It  is  incorrect 
to  speak  of  a  group  or  a  molecule  being  oxidized,  the  change 
actually  taking  place  with  one  atom  in  the  group  or  mole- 
cule whose  reactions  are  being  followed  and  perhaps  for  this 
reason  giving  the  impression  that  the  group  of  which  it 
forms  a  part  is  being  oxidized.  The  same  is,  of  course,  true 
for  reduction.  It  is  permissible  to  speak  of  a  group  as  pre- 
dominatingly positive  or  negative,  but  if  the  predominating 
charge  changes,  it  is  because  of  the  changes  in  the  charges 
of  one  or  more  of  the  atoms  making  up  the  group.  If  oxida- 
tion takes  place  in  a  reaction  in  the  sense  that  a  given 
atom  loses  one  or  more  negative  electrons,  then  it  is  neces- 
sary that  some  other  atom  in  one  of  the  molecules  taking 
part  in  the  reaction  must  be  reduced  (gain  one  or  more 
negative  electrons)  to  a  corresponding  extent. 

A  simple  reaction  which  may  be  mentioned  first  is  that  in 
which  a  metal  replaces  another  one  combined  as  a  salt. 
For  example,  if  metallic  sodium  is  fused  with  magnesium 
chloride,  metallic  magnesium  and  sodium  chloride  are 

190 


SOME  OXIDATION-REDUCTION  REACTIONS.       191 
formed  according  to  the  equation 

2Na  +  MgCl2  =  Mg  +  2NaCl. 

Such  reactions  are  common  in  inorganic  chemistry  and 
serve  for  the  preparation  both  on  a  laboratory  and  on  an 
industrial  scale  of  a  number  of  metals.  If  this  reaction 
takes  place  in  solution,  as  for  example  when  zinc  is  immersed 
in  a  solution  of  copper  sulfate,  forming  zinc  sulfate  and 
copper,  while  the  formulation  of  the  mechanism  of  the 
reaction  is  not  quite  as  simple  as  in  the  first  case,  the  oxida- 
tion-reduction changes  are  the  same.  Such  reactions  also 
are'  very  common,  and  are  the  source  of  electric  currents 
in  galvanic  cells  using  various  combinations  of  metals  and 
solutions,  the  electromotive  forces  under  certain  conditions 
being  a  measure  of  the  affinity  of  the  chemical  reaction 
taking  place. 

These  simple  and  well-known  reactions  of  inorganic 
chemistry  are  paralleled  in  organic  chemistry  by  the  Wiirtz 
and  Fittig  syntheses  and  the  Barbier-Grignard  reaction. 
The  Wiirtz  and  Fittig  syntheses  may  be  formulated  in  most 
general  terms  as  follows: 

RX  +  R'Y  +  2Me  =  RR'  +  MeX  +  MeY,        (1) 

in  which  R  and  Rr  represent  hydrocarbon  radicals  (aliphatic 
or  aromatic)  X  and  Y  halogen  atoms,  and  Me  a  metal  such 

o 

as  sodium.  The  symbol  Me  signifies  an  uncharged  or  un- 
combined  atom  of  the  metal.  In  the  Wiirtz  synthesis, 
aliphatic  hydrocarbon  halide  and  sodium  are  used,  as  for 
example : 

2CH3I  +  2Na  =  H3CCH3  +  2NaL  (2) 

(«OO) 

In  this  reaction  the  neutral  sodium  atoms  are  oxidized, 
at  the  same  time  that  a  carbon  atom  of  one  of  the  methyl 
iodide  molecules  is  reduced  two  units  of  valence  from 


192  CHEMICAL  REACTIONS. 

—  3+1=—  2  to  —  4.  The  analogy  to  the  inorganic 
reactions  outlined  is  evident.  In  the  same  way,  the  Fittig 
synthesis  deals  with  an  aromatic  halide  and  an  aliphatic 
halide,  as  for  example: 

C6H5Br  +  C2H5Br  +  2Na  =  C6H5C2H5  +  2NaBr.     (3) 

The  reaction  is  similar  to  the  Wiirtz  reaction,  but  the 
distribution  of  the  valence  electrons  or  the  charges  on 
the  separate  atoms  are  not  known  with  the  same  certainty. 
In  these  reactions,  only  the  initial  and  final  substances 
have  been  indicated.  It  is  possible  that  the  actual  mechan- 
ism of  the  reaction  is  not  so  simple  and  that  it  takes  place 
in  several  stages.  Evidence  for  this  view  is  to  be  found 
in  an  analogous  reaction,  in  which  magnesium  is  used  in 
place  of  sodium.  This  reaction  can  be  used  in  a  great 
number  of  syntheses  and  is  generally  known  as  the  Barbier- 
Grignard  reaction.  The  ordinary  formulation  is  as  follows  : 

RI+Mg=Mg<Jl;  Mg^+R'^Mgls+RR'.      (4) 


The  presence  of  some  solvent  such  as  ether,  dimethyl- 
aniline,  etc.,  is  necessary  for  the  reaction  to  proceed  with 
measurable  speed  or  at  all.  Instead  of  a  molecule  R'l 
taking  part  in  the  second  step  of  the  reaction,  a  great 
variety  of  other  substances  may  be  used  and  various  com- 
pounds synthesized.  The  reader  is  referred  to  appropriate 
text-  and  laboratory  books  of  organic  chemistry  for  these. 
The  formulation  of  equation  (4)  using  the  electron  concep- 
tion of  valence  would  be  as  follows: 

o  +-,*I          -H-y^I  4-4/1        +     -         ++/I          -f       — 

Mg=Mg^  =Mg(          Mg'+R-I=Mg/      +R    R       (5) 

XR  XR  VR  V 

(a) 

The  first  action  consists  of  the  combination  R+I~~  and 
atomic  uncharged  magnesium.  The  possible  intermediate 


SOME  OXIDATION-REDUCTION  REACTIONS.       193 

product  (a)  is  given  and  may  represent  the  first  stage  of 
combination  and  perhaps  be  equivalent  to  a  combination 
such  as  would  be  produced  by  the  force  fields  of  Baly  or 
some  similar  view  as  discussed  in  some  detail  in  an  earlier 
chapter.  In  the  formation  of  the  definite  compound 

++   /i  I"" 

Mg\^-R_,  the  magnesium  has  been  oxidized  two  units  of 

valence  and  one  of  the  carbon  atoms  of  the  group  R  reduced 
two  units  of  valence.  The  second  step  of  the  reaction 
consists  of  a  simple  reaction  involving  ultimately  an  ex- 
change without  oxidation  or  reduction.  As  stated  before, 
a  number  of  substances  may  take  part  here.  The  net 
result  is  a  reaction  analogous  to  the  reactions  just  described 
with  the  added  interest  that  intermediate  products  have 
been  isolated  here  which  were  not  possible  in  other  cases. 
Because  of  these  intermediate  products,  it  has  also  been 
possible  to  develop  the  mechanism  of  such  reactions  some- 
what farther  and  to  bring  out  further  analogies  between 
inorganic  and  organic  reactions  (cf.  in  this  connection 
J.  M.  Nelson  and  W.  V.  Evans,  Jour.  Amer.  Chem.  Soc. 
39,  82  (1917)).  It  was  stated  that  ether  or  some  similar 
solvent  was  necessary  for  the  Barbier-Grignard  reaction 
to  take  place.  The  ether  takes  part  in  the  reaction  and 
undoubtedly  forms  onium  (molecular)  compounds  with  the 
reacting  molecules.  It  plays  the  same  part  in  these  re- 
actions that  water  plays  in  the  reactions  involved  in  galvanic 
cells.  This  is  shown  clearly  by  the  following  measurements 
of  the  resistances  of  a  number  of  solutions: 

RESISTANCE  IN  OHMS  (ORDINARY  CONDUCTIVITY  APPARATUS). 

Ether above  1  X  107 

Ether  containing  ethyl  bromide above  1  X  107 

Ether  containing  1.2  gms.  Mg  as  Grignard  reagent 

(MgC2H5Br)  per  100  c.c 7.1  X  103 

Same  with  0.3  mg.  Mg 1.0  X  105 

0.02  M  KC1  aqueous  solution 1.26  X  102 


194  CHEMICAL  REACTIONS. 

A  cell  constructed  with  magnesium  and  platinum  as  elec- 
trodes, and  a  dry  ethereal  solution  of  ethyl  bromide  contain- 
ing a  small  amount  of  previously  prepared  Grignard  reagent 
as  solution,  gave  electromotive  forces  of  from  0.5  to  1.5 
volts. 

These  and  similar  results  show  that  the  reactions  in 
aqueous  and  ethereal  solutions  are  strictly  analogous  and 
that  similar  chemical  forces  govern  all  chemical  reactions, 
organic  as  well  as  inorganic. 

The  reaction  involving  addition  to  a  double  bond  between 
two  carbon  atoms  was  discussed  very  briefly  in  the  pre- 
ceding chapter.  From  the  evidence  at  present  available, 
it  may  be  said  that  if  the  two  halves  of  the  molecule  do  not 
differ  too  greatly  in  such  compounds,  the  linking  may  be 

db  db 

represented  as  :  C^C  :  the  charges  indicated  being  only 
those  due  to  the  double  linking.  If  a  halogen  hydride  is 
added  to  such  a  linking,  it  is  not  necessary  to  assume  any 
oxidation  or  reduction  reaction  taking  place.  If,  however, 
an  element  is  added  which  in  the  stable  form  is  negative  to 
carbon,  as  for  example  chlorine,  then,  if  the  chlorine  is 
considered  to  be  in  the  state  of  neutral  atoms,  after  the 
addition  each  atom  will  have  been  reduced  one  unit  of 
valence,  or  if  a  chlorine  molecule  C1-»C1  is  considered  to 
have  reacted,  one  of  the  chlorine  atoms  will  have  been 
reduced  two  units  of  valence,  while  at  the  same  time,  one 
of  the  carbon  atoms  will  have  been  oxidized  two  units  of 

cl  ci 

valence  to  give  the  group  tt     t±  .    This  would  be  a  true 

oxidation-reduction  reaction.  Similarly,  if  hydrogen  were 
added  to  a  double  carbon  linking,  since  hydrogen  is  normally 
positive  toward  carbon,  the  hydrogen  would  be  oxidized 
and  one  of  the  carbon  atoms  reduced.  These  considerations 
refer  only  to  the  initial  and  final  compounds  of  the  reactions. 
Probably,  as  in  the  Barbier-Grignard  reaction,  intermediate 


SOME  OXIDATION-REDUCTION  REACTIONS.        195 

compounds  are  formed.    These  reactions  may  be  illustrated 
by  the  following  examples: 

C6H5  -  CH  =  CH  -  C6H5  +  2Na 

=  C6H5  -  CHNa  -  CHNa  -  C6H5,     (6) 
C6H5  -  CHNa  -  CHNa  -  C6H5  +  2H2O 

=  C6H5  -  CH2  -  CH2  -  C6H6  +  2NaOH, 

(W.  Schlenk,  J.  Appenrodt,  A.  Michael,  and  A.  Thai,  Ber. 

47,  473  (1914)), 

C6H6  -  CH  =  CH  -  C6H5  +  2Br 

=  C6H5  -  CHBr  -  CHBr  -  C6H5,     (7) 

C6H5  -  CHBr  -  CHBr  -  C6H5  +  2H2O 

=  C6H5  -  CH(OH)  -  CH(OH)  -  C6H5  +  2HBr. 

The  action  of  water  here  involves  neither  oxidation  nor 
reduction  as  far  as  can  be  told  and  is  a  simple  hydrolysis. 
On  the  basis  of  the  theoretical  developments,  the  simplest 
view  to  take  is  that  equation  (6)  part  1  involves  a  reduction 
of  one  carbon  atom  two  units,  and  equation  (7)  part  1  an 
oxidation  of  one  carbon  atom  two  units.  The  hydrolysis 
reactions  indicate  this  difference  also.  As  pointed  out 
at  the  end  of  Chapter  IX,  these  explanations  represent  the 
facts  most  nearly  at  the  present  time,  but  the  possibility 
exists  that  the  oxidation-reduction  changes  are  actually 
brought  about  by  the  reagents  added  in  the  attempt  to 
determine  the  structures,  water  in  the  present  instance. 
The  possibility  exists  and  must  be  borne  in  mind  even 
though  the  evidence  at  present  available  is  against  this 
explanation  and  in  favor  of  the  one  given  in  greater  detail. 
The  number  of  these  reactions  can  be  increased  in- 
definitely. The  addition  and  substitution  of  halogen  are 
among  the  most  common  of  the  reactions  in  organic  chem- 
istry. As  shown  here  and  also  in  Chapter  I  in  discussing 
polar  and  non-polar  valence,  they  are  actually  oxidation 
reactions,  carbon  being  oxidized.  The  reaction  may  be 


196 


CHEMICAL  REACTIONS. 


considered  to  be  analogous  on  the  one  hand  to  the  trans- 
formation of  ferrous  chloride  to  ferric  chloride  for  example, 
in  which  ferrous  iron  is  oxidized  to  ferric  iron  and  chlorine 
added,  and  on  the  other  hand  to  the  transformation  of  a 
compound  such  as  phosphine  to  phosphorus  trichloride  (if 
this  direct  transformation  could  be  carried  out  experi- 
mentally) in  which  the  phosphorus  is  oxidized  from  —  3 
to  +  3.  Reduction  reactions  may  be  treated  similarly  and 
need  not  be  taken  up  in  further  detail  here. 

These  reactions  take  place  as  a  rule  between  two  or  more 
reacting  molecules  in  which  in  the  ultimate  products  two 
or  more  atoms  have  changed  their  valence.  In  a  number 
of  decomposition  reactions  of  more  or  less  complex  sub- 
stances, an  intramolecular  oxidation  and  reduction  may 
take  place,  in  such  a  manner  that  one  atom  is  oxidized  and 
another  reduced  at  the  same  time  that  simpler  molecules 
are  formed.  A  simple  reaction  of  this  type  is  given  by  the 
decomposition  of  formic  acid  as  follows: 


H  +<v° 

HX°% 


=  H20  +  CO      (a), 


=  H2+C02    (6). 


(8) 


In  formic  acid  and  its  decomposition  products,  the  direc- 
tions of  the  valences  or  the  charges  on  the  atoms  are  fairly 
definitely  known;  as  definitely  perhaps  as  in  any  compound. 
The  formula  for  formic  acid  is  given  in  the  brackets  as  an 
equilibrium  between  the  two  tautomeric  forms  as  discussed 
in  some  detail  in  Chapter  II.  It  will  be  noticed  that  in 
both  formulas,  the  state  of  oxidation  of  the  carbon  atom  is 
the  same,  +  2.  Formic  acid  is  known  to  decompose  in 
two  ways;  (a)  carbon  monoxide  and  water  are  formed  and 


SOME  OXIDATION-REDUCTION  REACTIONS.       197 


(6)  carbon  dioxide  and  hydrogen  are  formed.  Reaction 
(a)  takes  place  by  warming  with  sulfuric  acid;  reaction  (b) 
by  heating,  or  in  the  presence  of  finely  divided  rhodium, 
ruthenium,  or  iridium.  It  is  probable  that  both  sets  of 
products  are  present  to  a  slight  extent  ordinarily,  but  that 
on  suitable  treatment  one  set  predominates.  The  products 
of  the  reaction  are  simple  so  that  the  states  of  oxidation  of 
the  various  atoms  in  the  molecules  are  known.  It  is 
evident  therefore,  that  reaction  (a)  involves  no  oxidation  or 
reduction  of  any  of  the  atoms  in  the  molecule,  and  that  in 
reaction  (b)  the  carbon  atom  of  the  formic  acid  is  oxidized 
two  units  of  valence  to  form  carbon  dioxide,  and  one  of  the 
hydrogen  atoms  reduced  two  units  of  valence  to  form  the 
neutral  hydrogen  molecule.  As  stated  in  previous  chapters, 
such  reactions  represent  in  reality  equilibria  and  it  may 
therefore  be  noted  that  the  reverse  of  reaction  (a)  to  form 
formic  acid  can  be  brought  about  with  carbon  monoxide 
and  sodium  hydroxide,  and  the  reverse  of  reaction  (b)  with 
potassium  or  sodium  amalgam,  carbon  dioxide,  and  mois- 
ture. 

The  decomposition  of  oxalic  acid  by  sulfuric  acid  or  heat 
is  analogous  to  reaction  (a)  with  formic  acid: 


OH 


CO 


44 

C02 


HO 


(9) 


No  oxidation  or  reduction  of  any  of  the  atoms  is  involved 
in  this  reaction.  That  such  reactions  are  not  peculiar  to 
carbon  compounds  is  shown  by  the  fact  that  the  analogous 
sulfur  compound,  dithionic  acid,  undergoes  a  similar  de- 
composition, as  follows: 

[H2S206]  =  SO2  +  SO3  +  H2O.  (10) 


198  CHEMICAL  REACTIONS. 

The  structural  formula  of  dithionic  acid  with  the  charges 
on  the  atoms  can  be  developed  in  the  same  way  as  with 
oxalic  acid. 

Some  more  complex  reactions,  involving  hydrocarbon 
groups  will  be  taken  up  next,  but  the  development  will 
follow  the  same  lines  as  in  the  reactions  just  outlined  to- 
gether with  the  general  principles  developed.  While  un- 
questionably the  reagents  added  influence  the  course  a 
reaction  takes  under  given  conditions,  these  reagents  are 
not  included  in  the  present  formulations.  It  is  intended 
to  bring  out  here  the  possible  changes  in  valence  of  certain 
atoms  (oxidation  or  reduction)  in  fairly  simple  reactions, 
so  as  to  lay  a  possible  foundation  for  a  future  general 
classification  of  such  oxidation-reduction  reactions  when  a 
knowledge  of  the  valence  of  the  atoms,  their  charges  under 
given  conditions,  and  their  oxidizing  potentials  or  affinity 
for  the  negative  electrons  shall  have  been  determined  more 
precisely,  especially  for  organic  compounds,  than  is  the 
case  at  present. 

The  decomposition  of  acetic  acid  may  be  formulated  in  a 
way  similar  to  that  of  formic  acid;  namely  as  follows: 


+1       +»   ,  . 

=HQCOH  +  CO  (a), 


=CH4  +  COS 


(11) 


The  formula  for  acetic  acid  is  represented  as  an  equilibrium 
between  the  two  tautomeric  structures  as  explained  in 
Chapter  II.  In  both  the  carbon  atom  of  the  car  boxy  I 
group  is  in  a  state  of  oxidation  of  +  2.  The  direction  of 
the  valence  between  the  carbon  atom  of  the  methyl  group 
and  that  of  the  carboxyl  group  is  given  by  the  consid- 


SOME  OXIDATION-REDUCTION  REACTIONS.       199 

eration  of  the  structures  of  the  organic  acids  and  their  ioniza- 
tion  constants  in  Chapter  IX.  It  was  shown  there  that 
malonic  acid  belonged  to  the  same  group  of  acids  as  chlor- 
acetic  acid,  only  one  of  the  carboxyl  group  hydrogen  atoms 
being  ionized  and  the  other  carboxyl  group  acting  as  a  nega- 
tive substituent.  The  valence  of  carboxyl  and  chlorine 
toward  the  carbon  atom  of  the  organic  acid  is  the  same,  and 
therefore,  until  definite  evidence  to  the  contrary  is  found,  in 
the  linking  between  the  carbon  atom  of  the  carboxyl  group 
and  that  of  the  methyl  in  acetic  acid,  the  latter  is  taken  to 
give  up  one  valence  electron  to  the  former  as  represented  in 
the  formula.  Reaction  (a)  takes  place  without  any  of  the 
atoms  in  the  molecules  changing  valence,  but  in  reaction  (6) 
the  carbon  atom  of  the  carboxyl  group  is  oxidized  two  units 
forming  carbon  dioxide,  and  the  carbon  atom  of  the  methyl 
group  is  reduced  two  units  forming  methane.  As  in  the 
reactions  described  in  Chapters  VI  and  VII,  the  principle  of 
mass  action  governs  to  a  great  extent  the  nature  of  the 
products  obtained  under  certain  given  conditions.  The 
reverse  of  these  reactions,  to  form  acetic  acid,  can  be  carried 
out;  for  example  in  reaction  (a)  with  carbon  monoxide  and 
sodium  methylate,  in  reaction  (6),  with  the  Barbier-Grignard 
reaction  using  carbon  dioxide. 

A  number  of  reactions  involving  simple  derivatives  of 
acetic  acid  may  be  formulated  similarly.  For  example,  with 
propionyl  chloride  (propionyl  is  used  instead  of  acetyl  to 
illustrate  the  simple  formation  of  an  olefin)  the  reaction  is 
formulated  as  follows: 


C2H5  -  C        =  C2H4  +  HC1  +  CO.  (12) 

In  this  reaction  no  oxidation  or  reduction  has  taken  place. 
There  does  not  appear  to  be  the  same  possibility  of  oxida- 
tion-reduction as  with  acetic  acid. 

The  reactions  of  an  ester  are  as  follows: 

14 


200  CHEMICAL  REACTIONS. 

=  ^COg  +  C2H6  +  C2H4  (a), 

+  2  (13) 

=   CO  +  H20+2C2H4     (ft). 

In  reaction  (a)  oxidation  of  the  carbon  of  the  carboxyl 
group  has  taken  place,  and  reduction  of  a  carbon  atom  of 
one  of  the  hydrocarbon  groups.  In  reaction  (6)  no  oxida- 
tion or  reduction  of  any  of  the  atoms  in  the  reacting  mole- 
cules has  taken  place. 

The  reactions  of  acetoacetic  ester  represent  a  somewhat 
more  complex  case,  but  can  be  treated  in  the  same  way. 
Acetoacetic  ester  may  decompose  in  two  ways;  on  treat- 
ment with  dilute  alkali  (boiling)  or  with  dilute  sulfuric 
acid,  it  undergoes  the  "ketonic  decomposition"  with  the 
formation  of  a  ketone,  an  alcohol,  and  carbon  dioxide; 
treatment  with  concentrated  alcoholic  alkali  results  in  the 
"acid  decomposition"  and  formation  of  acid  and  alcohol. 
These  transformations  may  be  formulated  as  follows: 

_3    _i       -3          _i  ~j       -3          _2       -3 

41    +8       +1          +3XO  +1          +2        +  1 

-    CH3-CO*-CH3+CO2+C2H5OH    (a), 
N/ 


(R)  "OC2H5 


nHO 


UO 


+3 


=  CH3C02H-fCH3C02H+C2HpOH(6), 
(R)  (Ri) 

Reaction  (a)  represents  the  ketone  decomposition,  reaction 
(b)  the  acid  decomposition.  R  and  RI  can  be  used  to 
represent  a  variety  of  different  groups.  The  exact  relation 
of  R  to  the  carboxyl  group  with  which  it  is  combined  is  of 
secondary  importance,  as  long  as  it  does  not  change  in 
the  course  of  the  reaction.  The  distribution  of  the  charges, 
or  the  valence  of  the  atoms  follows  from  the  principles 
already  given.  In  reaction  (6),  the  acid  decomposition, 
there  is  apparently  no  oxidation  or  reduction  involved. 
This  reaction  involves  the  use  of  concentrated  alcoholic 
alkali,  a  reagent  which  is  supposed  to  cause  or  assist  oxida- 


SOME  OXIDATION-REDUCTION  REACTIONS.       201 


tions  in  organic  reactions.  Whether  it  does  or  not,  in  this 
reaction  at  any  rate,  no  oxidation  appears  to  occur.  Pos- 
sibly it  influences  the  changes  occurring  by  removing  the 
acetic  acid  as  soon  as  formed  and  causing  the  reaction  to 
take  the  indicated  course  (6)  according  to  the  principle  of 
mass  action.  In  reaction  (a)  on  the  other  hand,  an  oxida- 
tion-reduction has  occurred,  analogous  in  every  respect  to 
the  oxidation-reduction  with  acetic  acid.  The  group 
CH3COCH2  in  the  former  corresponds  to  the  group  CH3  in 
the  latter;  in  the  former  the  product  acetone  corresponds 
to  the  product  methane  in  the  latter.  The  possibilities  of 
tautomeric  forms  and  intermediate  products  are  much 
greater  with  acetoacetic  ester  than  with  the  simple  acids, 
and  no  attempt  will  be  made  here  to  formulate  them. 

The  reaction  between  chloroform  and  alkali  in  which 
the  former  is  hydrolyzed  may  be  represented  as  follows: 


[HCC13~] 
L2H20  . 


=  HC02H  +  3HC1. 


.  (15) 


No  oxidation  or  reduction  is  involved  here.  In  order  to 
show  the  uncertainties  with  regard  to  some  apparently 
simple  reactions,  the  decomposition  of  trichloracetic  acid 
(which  may  take  place  on  heating  an  aqueous  solution) 
may  be  shown: 


+  3 

C1~C- 


or 


(a) 


(b) 


OH 


f  3 

HCC13  +  +C03 


The  question  which  arises  is  as  to  the  structure  of  trichlor- 
acetic acid;  whether  it  is  to  be  represented  by  formula  (a) 


202  CHEMICAL  REACTIONS. 

or  (6).  The  ionization  constant  does  not  give  any  clue, 
since  it  varies  too  greatly  with  the  dilution  to  permit  of 
classification.  The  small  difference  in  potential  between 
the  two  carbon  atoms  of  trichloracetic  acid  also  adds  to  the 
uncertainty  as  there  is  nothing  to  indicate  whether  one  is 
positive  or  negative  to  the  other.  If  formula  (a)  is  correct, 
no  oxidation  or  reduction  is  involved;  if  formula  (6)  is 
correct  then  the  carbon  atom  of  the  carboxyl  group  is 
oxidized  two  units  of  valence  and  the  other  carbon  atom 
reduced  two  units  of  valence  in  the  reaction.  As  stated, 
there  is  no  definite  evidence  to  indicate  the  true  nature  of 
the  reaction. 

The  reactions  of  benzenesulfonic  acid  have  been  of 
interest  in  connection  with  questions  of  valence  for  some 
time.  On  hydrolysis  with  acid,  benzene  and  sulfuric  acid 
are  formed,  with  alkali,  phenol  and  sulfite.  The  question 
of  oxidation  and  reduction  in  these  reactions  can  be  ap- 
proached best  by  considering  first  the  structure  of  the 
benzene  sulfonic  acid  as  developed  from  simple  principles 
and  analogies. 

In  the  first  place,  in  general  when  carbon  combines  with 
sulfur,  the  carbon  atom  loses  a  negative  electron  to  the 
sulfur  atom.  This  is  evident  from  the  relative  positions  of 
these  elements  in  the  Periodic  System.  In  the  second 
place,  in  the  development  of  the  structures  of  the  acids  in 
Chapter  IX,  it  was  found  that  benzoic  acid  belongs  to  the 
same  class  as  acetic  acid.  There  is  every  reason  to  believe 
that  in  these  acids,  the  carboxyl  group  as  a  whole  is  negative 
to  the  hydrocarbon  group  as  a  whole,  whatever  their  internal 
structures  may  be,  although  of  course  the  various  charges 
are  present  on  the  individual  atoms.  The  formation  of 
benzoic  acid  from  benzene  and  carbon  dioxide  might  then 
be  formulated  as  follows: 

[C6H6]-  <-  H+  +  Ca  =  [C6H5]+  ->  CftH.       (17) 


SOME  OXIDATION-REDUCTION  REACTIONS.       203 

A  reaction  of  this  kind  might  be  involved  in  the  Barbier- 
Grignard  reaction  with  the  formation  of  salicylic  acid  from 
phenol,  etc.,  without  considering  the  intermediate  products, 
but  only  the  compositions  and  structures  of  the  initial  and 
final  substances.  The  change  involves  the  reduction  of 
the  carbon  of  the  carbon  dioxide  and  the  oxidation  of  one 
of  the  carbon  atoms  of  the  benzene.  It  is  exactly  the 
same  change  as  was  shown  in  reaction  (116)  in  the  for- 
mation of  methane  and  carbon  dioxide  from  acetic  acid 
which  was  shown  to  be  an  oxidation-reduction  reaction. 

The  sulfonation  of  benzene,  in  which  80s  plays  a  similar 
part  to  that  of  the  CC>2  should  then  follow  the  same  rules. 
The  formulation  may  be  indicated  as  follows: 

[CeHg]-  <-  H+  +  S03  =  [C6H5]+  ->  S02  -»  OH.    (18) 

Here,  also,  the  reaction  may  be  considered  to  be  oxidation- 
reduction;  the  sulfur  being  reduced  from  +6  to  +  4 
(+5—1),  and  one  of  the  carbon  atoms  of  the  benzene 
ring  oxidized  correspondingly.  This  agrees,  also,  with  the 
directions  of  the  valences  as  deduced  from  the  Periodic 
System,  although  too  much  stress  must  not  be  laid  upon 
this  point. 

The  hydrolysis  reactions  of  benzene  sulfonic  acid  may 
now  be  indicated,  as  follows: 


(ACID)        C6H6<-H  +  SO3       (6), 

(19) 

+4 

(ALKALI)     CeHs-^OH  +  SC>2    (a). 


.SOS 
H 

These  decomposition  reactions  (the  formation  of  sulfuric 
acid  and  of  sulfite  is  not  given  in  the  equations  but  must 
be  understood  to  occur)  are  analogous  to  the  decomposition 
reactions  of  acetic  acid,  equations  (11).  Reactions  (a) 


204  CHEMICAL  REACTIONS. 

in  both  cases  involve  no  oxidation  or  reduction,  reactions 
(6)  are  oxidation-reduction  reactions.  The  detailed  exposi- 
tion with  benzene  sulfonic  acid  need  not  be  gone  into,  since 
it  follows  the  corresponding  changes  with  acetic  acid. 

Another  type  of  reaction  may  be  mentioned  here,  which, 
while  not  oxidation-reduction,  shows  some  of  the  possibili- 
ties in  the  way  of  relative  oxidizing  potentials  of  different 
atoms,  or  the  relative  affinities  of  the  atoms  for  valence 
electrons.  Silver  nitrite  and  sodium  nitrite  when  treated 
with  an  alkyl  halide  give  different  products.  With  the 
former,  a  nitro  compound  is  obtained  mainly;  with  the 
latter  a  nitrite  predominates.  While  according  to  the  older 
views,  this  would  point  to  different  structures  for  the  two 
nitrites,  according  to  the  principles  developed  in  this  book, 
the  explanation  of  these  differences  involves  tautomerism 
and  several  chemical  equilibria.  The  reaction  may  be 
given  in  general  terms  as  follows : 


Me-*- 


I 


O 


'/ 


MeX 


O 


H-RX^  _  (20) 

+  3^ 

MeX  +  Nj" 

^O^-R 

The  silver  and  sodium  nitrites  may  exist  in  tautomeric 
forms  as  shown  in  the  formula  and  outlined  in  Chapter  II. 
There  is  no  evidence  at  hand  at  present  to  show  which  form 
predominates  under  any  given  conditions.  When  the 
nitrite  is  treated  with  the  alkyl  halide  RX,  in  all  probability 
an  addition  compound  is  formed  which  is  not  given  in  the 
equations,  and  this  addition  compound  is  in  equilibrium 
with  the  two  sets  of  products  represented  by  equations  (a) 
and  (6).  There  is  no  oxidation  or  reduction  involved  in 
either  of  these  equations.  Unquestionably  both  sets  of 
products  are  obtained  with  any  metallic  nitrite.  Which 


SOME  OXIDATION-REDUCTION  REACTIONS.       205 

product  is  obtained  in  greater  amount  with  a  given  nitrite 
will  depend  upon  the  relative  oxidizing  potentials  of  the 
various  atoms  in  the  molecule.  This  is,  in  reality,  only  a 
different  way  of  stating  that  the  relative  amounts  of  the  two 
sets  of  products  depend  upon  the  chemical  affinity  or  the 
states  of  the  equilibria.  Because  of  the  similarity  of  the  reac- 
tions, it  would  not  be  expected  that  the  velocities  would  differ 
greatly,  but  this  possibility  must  also  be  kept  in  mind  as  pos- 
sibly the  dominating  factor  in  controlling  the  course  of  the  re- 
action observed.  To  speak  of  the  relative  oxidizing  poten- 
tials toward  oxygen  and  nitrogen  of  the  metal  instead  of 
the  chemical  affinities  does  not  add  directly  to  the  knowledge 
of  the  reaction  but  brings  it  into  line  with  the  newer  point 
of  view  developed  in  this  book,  and  may  aid  in  developing 
a  future  classification  of  such  reactions.  If  the  metal  is 
sodium  in  reaction  (20),  the  reaction  follows  course  (6) 
mainly,  if  silver,  course  (a).  It  may  be  possible  to  deter- 
mine the  relative  oxidizing  potentials  of  sodium  and  silver 
toward  oxygen  and  nitrogen  in  these  reactions  by  suitable 
measurements  of  the  equilibria  under  comparable  condi- 
tions. This  point  of  view  may  evidently  be  extended  to  a 
number  of  other  reactions  which  show  similar  changes. 

Finally,  a  classification  of  chemical  reactions  which  in- 
cludes all  reactions  in  a  general  scheme  based  upon  the 
valences  and  changes  in  the  valences  of  the  atoms  in  the 
reacting  molecules  may  be  given.  In  every  reaction,  either 

I.  The  algebraic  sum  of  the  positive  and  negative  charges 
on  a  definite  atom  of  the  molecules  involved  changes;  or 

II.  The  algebraic  sum  of  the  positive  and  negative  charges 
on  a  definite  atom  of  the  molecules  involved  remains  con- 
stant. 

If  I,  the  algebraic  sum  changes;  either,  A,  the  number 
of  negative  electrons  on  the  atom  in  question  is  increased, 
or  the  number  of  positive  charges  on  the  atom  is  decreased 
(or  reduction) ;  or,  B,  the  number  of  negative  electrons  on. 


206  CHEMICAL  REACTIONS. 

the  atom  is  decreased,  or  the  number  of  positive  charges  on 
the  atom  is  increased  (oxidation). 

If  II,  the  algebraic  sum  remains  constant;  either,  A,  the 
arithmetical  sum  of  the  positive  and  negative  charges  on 
the  atom  in  question  changes;  i.e.,  the  atom  in  question 
gains  or  loses  the  same  number  of  positive  and  negative 
charges  simultaneously  (molecular  or  onium  compound 
formation);  or,  B,  the  arithmetical  sum  of  the  positive 
and  negative  charges  on  the  atom  in  question  remains 
constant;  i.e.,  the  electric  charge  on  the  atom  in  question 
remains  unchanged. 

To  sum  up:  In  every  reaction — 

I.  If  the  algebraic  sum  of  the  positive  and  negative 
charges  on  a  definite  atom  of  the  molecules  changes;  either, 
At  the  number  of  negative  electrons  on  the  atoms  increases; 
or,   B,   the   number  of  negative   electrons  on  the   atom 
decreases; 

II.  If  the  algebraic  sum  of  the  positive  and  negative 
charges  on  the  atom  remains  constant;    either,  A,  the 
arithmetical  sum  changes;    or,  B,  the  arithmetical  sum 
remains  constant. 

Applied  to  chemical  reactions,  IA  includes  reduction 
reactions,  IB  oxidation  reactions,  HA  molecular  or  onium 
compound  formation  and  decomposition,  IIB  metatheses 
in  which  none  of  the  changes  IA,  IB,  or  IL4  takes  place. 
Stated  slightly  differently,  the  classification  includes  re- 
actions involving  reduction,  oxidation,  molecular  or  onium 
compound  formation  and  decomposition,  and  simple  re- 
placement or  rearrangement. 


INDEX 


Authors'  Names  in  roman,  Subjects  in  italics 


Abel,  E.,  72 

Abegg,  E.,  98 

Acetic   acid   decomposition,   158, 

198,  190,  201 
Acetoacetic   ester   decomposition, 

200,  201 

Acetylenes,  145,  181 
Acree,  S.  F.,  128 
Adsorption,  69 
Aldol  condensation,  111,  115,  120, 

125 
AlTcyl  bolides,  136-143,  145-147, 

156,  160,  162,  204 
Aluminium      compounds      (com- 
plex), 105,  106 

Amides,  121,  156,  157,  163-165 
Amines,    53,   65,    121,    142,    146, 

156,  160,  161-103 
Ammoniates,  21,  25,  26,  28,  29, 
30,  31,  33,  34,  36,  38,  45,  46, 
48,   57,   58,   89,   90,   136,   137, 
143,  156,  159,  160,  161,  163 
'  'Anomalous ' '     compounds,     24, 

25,  48,  136 
Anschiitz,  W.,  155 
Appenrodt,  J.,  195 
Armstrong,  E.  F.,  68 
Arrhenius,  S.,  10',  15,  41,  45,  128 
Aschan,  I.,  105 
Atomic  theory,  1,  2,  3 
Autenreith,   W.,    155 
"  Auxiliary      (secondary)     val- 
ence," 2'2,  23,  24,  30,  31,  32, 
37 

Baeyer,  A.,  25,  26 


Baly,  E.  C.  C.,  22,  23,  32,,  67, 

193 

Bancroft,  W.  D.,  72 
Barbier,  P.,  191,  192,  193,  194, 

199,  203' 
Bartier-Grignard    reaction,    191, 

192-194,  199,  203 
Barker,  T.  V.,  34 
Baume,  G.,  137,  142,  150 
Belial,  A.,  150 
Benzene  nucleus,   18<2,   183,   188, 

189,  20'3 

Benzenesulfonic  acid  decomposi- 
tion, 202-204 
Benzidine     rearrangement,     109, 

112,  116,  122 
Benzoic  acid  decomposition,  202, 

203 
Bernthsen,  A.,  129 

Berthelot,  M.,  176 

Berzelius,  J.,  169 

Bethmann,  H.  G.,  176 

Boedtker,  E.,  104 

Boeseken,  J.,  97,  98,  99 

Bone,  W.  A.,  176 

Booge,  J.  E.,  150 

Bragg,  W.  H.,  vii,  34 

Bragg,  W.  L.,  vii,  34 

Branch,  G.  E.  K.,  vi,  39,  158 

Bray,  W.  G.,  vi,  39 

Bredig,  G.,  72,  128 

Brown,  A.,  681 

Brown,  H.  T.,  68 

Briihl,  J.,  92 

Brunei,  E.  F1.,  vi 

Brussow,  S.,  142 

Buehbock,  G.,  56 

Butleroff,  A.,  143 


207 


208 


INDEX. 


Carpenter,  C.  D.,  27 

Chemical  affinity,  4,  5,  6,  7,  8,  14, 

32,  78,  132L-134,  168',  109,  170, 

191,  205 

Chemical  energy,  3,  4,  5,  14 
Chemometer,  168 
Chojnacki,  C.,  137 
Classification    of   reactions,    205, 

206 

Collie,  J.  N.,  25,  26 
Color,  105,  128 
Combes,  A.,  109 
Cone,  L.  H.,  27 
Co-ordination  number,  31,  33,  34, 

46,  47,  48,  49,  50,  51,  52,  58, 

83 

Crafts,  J.  M.,  95,  103 
Crehore,  A.  C.,  34 
Crum  Brown,  A.,  176 
Cullen,  O.  E.,  68 

Dakin,  H.  D.,  68 

Dawson  H.  M.,  128 

de  Coninck,  W.  O.,  158 

de  Forcramd,  E..  137 

Derick,  C.  G.,  131,  132,  133,  134 

Desgrez,  A.,  150 

Diazo  reaction,  116-119,  122 

Dilution  law,  53,  173,  178 

Dithionio      add      decomposition, 

158,  197 
Double  "bond  isomerism,  180,  181, 

184-1816,  187,  188,  194 
Drucker,  K.,  176 
Duclaux,  J.,  68 
Dushman,  S.,  vi 

Electroisomers,  15 

Electrolytic  dissociation,  10,  15, 
28,  29,  35,  36,  41, 42,  45, 47, 48, 
49,  52,  53,  54,  55-57,  82,  83, 
86-88,  90-92,  123,  124,  125, 
126,  127-130,  139,  140,  148, 
152,  156,  169,  172,  173 


Electromerism,  187,  188,  189 
Electromotive    force,     168,    169, 

170,  191,  194 
Electron,   12,  17,   167,   169,  170, 

172,   183,  187,   188,  189,   190, 

192,  198,  205,  206 
Electronic  valence,  v,  vi,  10,  11, 

12,  13,  18,  24,  32,  42,  49,  54, 

56,    169,    170,    171,    172,    173, 

188,  192,  199,  204 
Eltekoff,  M.,  142 
Emory,  W.  O.,  156 
Energy,    capacity   and   intensity 

factors,  3^5 
Engel,  E.,  152 
Enzymes,  67,  68,  69 
Ephraim,   F.,   89,   90 
Equilibria,  chemical,   2,  6,   7,  9, 

53,  54,  60,   71-75,   78,  82,  86, 

88,  93,  101,  102,  108.,  112,  113, 

122,   129,   130,   138,   140,   144, 

146,  149,  150,  197,  204,  20<5 
Esterification,  63,  119,  121,  123, 

125,  147,  150-154 
Etherification,  63,  109,  110,  121, 

125,  147,  155 
Euler,  H.,  176 
Evans,  W.  V.,  127,  193 

Talk,   K.   G.,   62,   68,   127,    173, 

18/7 

Findlay,  A.,  26 
Fischer,  E.,  68 
Fischer,  F.,  105 
Kttig,  E.,  191,  192 
Fittig  synthesis,  191,  192 
"Force  fields,"  23,  32,  37,  193 
Formic  acid  decomposition,   196, 

197 

Franke,  E,,  176 
Franklin,  E.  C.,  145 
Free  energy,  4,  5,  6,  7,  8,  18,  75, 

132-134,  168 
Friedel,  C.,  25,  95,  103 


INDEX. 


209 


Friedel-Craft  s  reaction,  64,  95- 
106,  108,  111,  115,  117,  120, 
125,  138,  146 

Fry,  H.  S.,  v,  187,  189 

Gasiorowski,  K.,  163 

Gatterman,  L.,  103 

Genequand,  P.,  114 

Germann,  A.  F.  O.,  137 

Geyer,  A.,  155 

Gibbons,  W.  A.,  27 

Gibbs,  W.,  7 

Glendenning,  T.  A.,  68 

Goldschmidt,  H.,  128.,  150,  163 

Gomberg,  M.,  27 

Grignard,  V.,  126,  127,  160,  191, 

192,  193,  194,  199,  203 
Grignard  reagent,  126,  127,  160, 

193,  194 

Gulewitsch,  W.,  9'8 
Gustavson,  G.,  96,  97,  146 
Guye,  P.  A.,  98 

Hantzsch,  A.,  120,  176 

Haussermanni,  J.,  161 

Helmholtz,  H.,  7 

Hofmann,  A.  W.,  53,  162 

Hofmann,  K.  A.,  26 

Hohmann,  C.,  148,  149 

Holleman,  A.  F.,  109,  123 

Hoogewerff,  S.,  26 

Hydrates,  21,  26,  27,  28,  33,  36, 
37  38,  45,  46,  47,  48,  49,  51, 
52,  56,  57,  58,  81,  82,  83,  89, 
120,  141,  147,  151,  156,  157, 
159,  160 

Indicators,  129,  130 

lonization  constant,  53,  54,  147, 

148,  173-182,  202 
Isbekow,  W.  A.,  90,  91,  92 

Jacobson,  P.,  136,  137,  157,  165 
Jones  L.  W.,  v,  187 
Jones,  W.  J.,  72 


Kachler,  J.,  137 

Kamm,  O.,  133 

Kauffmann,  H.,  vi 

Kendall,   J.,   27,   105,   125,   148, 

150 

Kipping,  F.  S.,  102,  103 
Kleber,  C.,  176 
Klein,  D.,  66 
Klemensiewicz,  Z.,  91 
Koch,  J.  A.,  103 
Kohler,  E.  P.,  9-8 
Kondakow,    J.,    136,    145,    146, 

149 

Konowalow,  D.,  145,  147,  154 
Krapivin,  S.,  103 
Kraus,  C.  A.,  145 

Lang,  B.,  98,  99 
Langmuir,  I.,  vi 
Lapworth,  A.,  72,  128 
Lecco,  M.,  24 
Lercynska,  I.,  105 
Lermontoff,  J.,  142 
Lewis,  G.  N.,  v,  vi,  39 
Lichty,  D.  M.,  176 
Li-ben,  A.,  142 
Lifsehitz,  J.,  128 
Loremz,  E.,  91 

Maass,  O.,  27 

Mclntosh,  D.,  26,  27 

Maihle,  A.,  137,  138 

' '  Main      (principal )      valence, ' ' 

31,  32 

Markownikoff,  W.,  114 
Martinsen,  H.,  113 
MeUor,  J.  W.,  67,  74 
Mendeleeff,  D.,  3,  20,  172 
Menfichutkin,  B.  N.,  65,  97,  98, 

99  147 

Menten,  M.  L.,  68 
Merz,  V.,  163 
Meyer,  V.,   24,      136,   137,   157, 

165 
Michael,  A.,  195 


210 


INDEX. 


Michael,  Arthur,  138,  185 
Michaelis,  A.,  104 
Michaelis,  L.,  68 
MiUikan,  E.  A.,  12 
Miolati,  A.,  176 
Molecular  theory,  1,  2,  3 

Nef,  J.  TL,  99,  110,  111 
Nelson,  J.  M.,  v,  vi,  62,  68,  70, 

127,  187,  193 

Nernst  W.,  92,  148,  149,  168,  169 
Niggeman,  H.,  105 
Nitration,  108,  109,  110-115,  122 
Nitrite  reactions,  204,  205 
Northrop,  J.  H.,  70 
Noyes,  A.  A.,  130 
Noyes,  W.  A.,  v,  184 

Olefinates,  136,  137,  143,  147, 
150,  156,  159,  160,  161,  165 

Onium  compounds,  27,  28,  30,  32, 
38,  57,  81,  88,  89,  105,  106, 
112,  193,  206 

Onium  valence,  30,  32,  37,  38,  57 

Oppenheim,  A.,  136 

Organic  acids  (structures'),  156- 

158,  173-184 

Ostwald,  W.,  53,  129,  168,  173, 

176,  178 
Oxalic   acid   decomposition,    158, 

197 
Oxonium  salts,  25,   26,  48,   147, 

159,  160,  161,  177 

Pamfil,  G.  P.,  150 

Panek,  C.,  104 

Partial  valence,  v,  133 

Patten,  H.  E.,  92 

Periodic   system,   3,   10,    13,   20, 

172,  202,  203 
Perrier,  G1.,  96 
Perrin,  J.,  3 
Phase  rule  diagrams,  26,  58,  97, 

98,  162 
Pictet,  A.,  105,  114 


Platinum-ammonia  compounds, 
28-31,  33,  34,  36,  38,  39,  44, 
58,  188 

Plotnikoff,  V.  A.,  26,  92,  98,  103 

Polar  and  non-polar  valence,  vi, 
15,  16,  17,  19,  87,  135,  167, 
195 

Potentials,  oxidizing  and  re- 
ducing, 13,  14,  116,  169,  170, 
172,  173,  184,  187,  198,  202, 
204,  205 

Precht,  H.,  136 

Priiis,  H.  J.,  103 

Reaction  velocity,  1,  6,  9,  60,  61, 
62,  65,  66,  69,  70,  71,  73,  76, 
79,  81,  97,  106,  108,  113,  114, 
122,  123,  124,  137,  138,  142, 
147,  148,  149,  152,  160,  172, 
205 

Eosanoff,  M.  A.,  72 

Eossi,  A.,  142 

Sabatier,  P.,  64,  137,  138 
Sackur,  O.,  91 
Salt  hydrolysis,  126 
Scheffer,  F.  E.  C.,  29 
Schlenk,  W.,  195 
Sehmidlin,  J.,  98,  99 
Selivanow,  T.,  184 
Senter,  G.,  128 
Smith,  A.,  138' 
Smith,  W.  A.,  176 
Snethlage,  H.  O.  S.,  128 
Sprankling,  C.  H.  G.,  176 
Stark,  J.,  vi 

Stereochemical  capacity,  vii,  34 
Stieglitz,  J.,  v,  128,  129,  150 
Stobbe,  H.,  26 
Stohmann  F.,  176 
Strauss,  F.,  26 
Sudborough,  J.  J.,  176 
Sugiura,  K.,  68 

Sulfuric  acid  condensations,  107, 
111,  125,  143,  144,  145 


INDEX. 


211 


Szyszkowski,  B.,  176 

Tautomerism,  32,  38,  39,  40,  43, 
44,  46,  52,  81,  82,  92,  112,  113, 
117,  129,  130,  131,  147,  156, 
187,  196,  198,  201,  204 

Taylor,  H.  S.,  128 

Thai,  A.,  195 

Thiele,  J.,  v,  26,  132 

Thomson,  J  J,,  v,  10,  12,  20,  92 

Tickle  T.,  26,  26 

Tissier,  L.,  130 

Tolloczko,  S.,  91 

Trichlor  acetic  acid  decomposi- 
tion, 201,  202 

Unsaturation,  23,  64,  66,  79,  92, 
115,  127,  132,  135,  136,  137, 
145,  180,  181 

Valence,  v,  1,  3,  4,  5,  8,  9,  10, 
11,  12,  15,  17,  18,  19,  20,  21, 
22,  24,  30,  32,  34,  51,  52,  57, 
83,  105,  135,  166,  167,  169, 
170,  171,  173,  174,  183,  184, 
185,  187,  188,  191,  193,  194, 
196,  197,  198,  199,  200,  202, 
203,  204,  205 

Valence  Unkings,  3,  9,  20,  34,  64, 
167,  170,  171,  172 

van  Dorp,  W.  A.,  26 

van  Slyke,  D.  D.,  68 


van't  Hoff,  J.  H.,  7,  74 
Varet,  B.,  103 
Vienna,  G.,  103 
Villiger,  V.,  25,  26 
Vorlander,  D.,  26 
Vosburgh,  W.  C.,  68 

Wachs,   C.,   163 

Walden,  P.,  176 

Walker,  J.,   176 

Walker,  J.  W.,  87,  99,  104 

Washburn  E.  W.,  56 

Wecker,  E.,  10-5 

Wedekind,  F.,  161 

Werner,  A.,  vi,  21,  23,  24,  28,  30, 
31,  32,  34,  35,  38,  42,  44,  50, 
54,  83,  90,  124,  152,  187,  188 

Wieland,  H.,  105 

Wildermann,  M.,  142 

Willstatter,  E.,  114 

Wilsmore,  N.  T.  M.,  169 

Wroczynski,  A.,  98 

Wiirtz,  A.,  191,  192 

Wurtz  synthesis,  191,  192 

Zinc  chloride  condensations,  106, 
107,  125,  145,  146,  149,  150, 
163 

Zones,  inner  and  outer,  31,  32, 
35,  37,  38,  44,  45,  46,  47,  49, 
50,  52,  54,  56,  57,  58,  81 


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